The Collaborative International Dictionary of English v.0.48:

Blockade \Block*ade"\, v. t. [imp. & p. p. Blockaded; p. pr. &
   vb. n. Blockading.]
   1. To shut up, as a town or fortress, by investing it with
      troops or vessels or war for the purpose of preventing
      ingress or egress, or the introduction of supplies. See
      note under Blockade, n. "Blockaded the place by sea."
      --Gilpin.
      [1913 Webster]

   2. Hence, to shut in so as to prevent egress.
      [1913 Webster]

            Till storm and driving ice blockade him there.
                                                  --Wordsworth.
      [1913 Webster]

   3. To obstruct entrance to or egress from.
      [1913 Webster]

            Huge bales of British cloth blockade the door.
                                                  --Pope.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Blockade \Block*ade"\, n. [Cf. It. bloccata. See Block, v. t.
   ]
   1. The shutting up of a place by troops or ships, with the
      purpose of preventing ingress or egress, or the reception
      of supplies; as, the blockade of the ports of an enemy.
      [1913 Webster]

   Note: Blockade is now usually applied to an investment with
         ships or vessels, while siege is used of an investment
         by land forces. To constitute a blockade, the investing
         power must be able to apply its force to every point of
         practicable access, so as to render it dangerous to
         attempt to enter; and there is no blockade of that port
         where its force can not be brought to bear. --Kent.
         [1913 Webster]

   2. An obstruction to passage.
      [1913 Webster]

   3. (physiology) interference with transmission of a
      physiological signal, or a physiological reaction.
      [PJC]

   To raise a blockade. See under Raise.
      [1913 Webster]

WordNet (r) 3.0 (2006):

blockade
    n 1: a war measure that isolates some area of importance to the
         enemy [syn: blockade, encirclement]
    2: prevents access or progress
    v 1: hinder or prevent the progress or accomplishment of; "His
         brother blocked him at every turn" [syn: obstruct,
         blockade, block, hinder, stymie, stymy,
         embarrass]
    2: render unsuitable for passage; "block the way"; "barricade
       the streets"; "stop the busy road" [syn: barricade,
       block, blockade, stop, block off, block up, bar]
    3: obstruct access to [syn: blockade, block off]
    4: impose a blockade on [syn: blockade, seal off]

Moby Thesaurus II by Grady Ward, 1.0:

379 Moby Thesaurus words for "blockade":
   Jacksonian epilepsy, Rolandic epilepsy, abdominal epilepsy, access,
   acquired epilepsy, activated epilepsy, affect epilepsy,
   afterthought, akinetic epilepsy, apoplexy, arm, armor, armor-plate,
   arrest, arrestation, arrestment, attack, autonomic epilepsy, ban,
   bank, bar, bar out, barricade, barrier, barring, battle, beleaguer,
   beleaguerment, beset, besetment, besiege, besiegement, bind,
   blank wall, blind alley, blind gut, block, block up, blockade,
   blockading, blockage, blocking, bolt, bottleneck, bound, box in,
   boycott, bulwark, bung, bureaucratic delay, cage, cardiac epilepsy,
   castellate, catch, caulk, cecum, censorship, chamber, check, chink,
   chock, choke, choke off, choke up, choking, choking off,
   circumscription, clog, clog up, clogging, clonic spasm, clonus,
   close, close in, close off, close tight, close up, closing,
   closing up, closure, compass, confinement, congest, congestion,
   constipate, constipation, constrict, constriction, contain,
   convulsion, coop, coop in, coop up, cordon, cordon off, cordoning,
   cork, corral, cortical epilepsy, costiveness, count out, cover,
   cramp, crenellate, crowd, cul-de-sac, cursive epilepsy, curtain,
   cut off, dam, dam up, dead end, debar, debarment, debarring, delay,
   delayage, delayed reaction, demarcation, detainment, detention,
   determent, deterrent, difficulty, dig in, diurnal epilepsy, dog,
   double take, dragging, drawback, eclampsia, embargo, embattle,
   embolism, embolus, encircle, encirclement, enclose, enclosure,
   encompass, encompassment, enshrine, entrench, envelop, envelopment,
   epilepsia, epilepsia gravior, epilepsia major, epilepsia minor,
   epilepsia mitior, epilepsia nutans, epilepsia tarda, epilepsy,
   exception, exclude, exclusion, falling sickness, fence, fence in,
   fill, fill up, fit, fixation, focal epilepsy, foot-dragging,
   fortify, foul, freeze out, frenzy, garrison, gorge, grand mal,
   halt, hampering, hang-up, harass, harry, haute mal, hazard,
   hedge in, hem in, hindering, hindrance, hitch, holdback, holdup,
   house in, hurdle, hysterical epilepsy, ictus, ignore, immurement,
   impasse, impediment, impound, imprison, imprisonment,
   inadmissibility, incarcerate, incarceration, include, inclusion,
   infarct, infarction, inhibition, injunction, interference, interim,
   interruption, invest, investment, jail, jam, joker, keep out,
   kennel, lag, lagging, larval epilepsy, laryngeal epilepsy,
   laryngospasm, latent epilepsy, lay siege to, leaguer, leave out,
   let, lock, lock out, lockjaw, lockout, logjam, man,
   man the garrison, matutinal epilepsy, menstrual epilepsy, mew,
   mew up, mine, moratorium, musicogenic epilepsy,
   myoclonous epilepsy, narrowing, negativism, nocturnal epilepsy,
   nonadmission, nuisance value, objection, obstacle, obstipate,
   obstipation, obstruct, obstruction, obstructionism, obstructive,
   occlude, occlusion, omission, omit, one small difficulty,
   opposition, ostracize, pack, palisade, paperasserie, paroxysm,
   pass over, pause, pen, pen in, petit mal, physiologic epilepsy,
   pincer movement, plug, plug up, pocket, preclude, preclusion,
   prohibit, prohibition, psychic epilepsy, psychological block,
   psychomotor epilepsy, quarantine, rail in, red tape, red-tapeism,
   red-tapery, reflex epilepsy, reject, rejection, relegate,
   relegation, repression, reprieve, repudiate, repudiation,
   resistance, respite, restraint, restriction, retardance,
   retardation, retardment, roadblock, rotatoria, rub, sealing off,
   seizure, send to Coventry, sensory epilepsy, serial epilepsy,
   setback, shrine, shut in, shut off, shut out, shut tight, shut up,
   shutdown, shutting, shutting up, siege, slow-up, slowdown,
   slowness, snag, soften up, spasm, spile, squeeze, squeeze shut,
   stable, stanch, stay, stay of execution, stench, stifle, stop,
   stop up, stoppage, stopper, stopple, strangle, stranglehold,
   strangulate, strangulation, stricture, stroke, stuff, stuff up,
   stumbling block, stumbling stone, suffocate, suppression, surround,
   suspension, taboo, tardy epilepsy, tetanus, tetany, throes,
   thromboembolism, thrombosis, tie-up, time lag, tonic epilepsy,
   tonic spasm, torsion spasm, traumatic epilepsy, trismus,
   ucinate epilepsy, vertical envelopment, visitation, wait, wall,
   wall in, wrap, yard, yard up



Bouvier's Law Dictionary, Revised 6th Ed (1856):

BLOCKADE, international law. The actual investment of a port or place by a
hostile force fully competent to cut off all communication therewith, so
arranged or disposed as to be able to apply its force to every point of
practicable access or approach to the port or place so invested.
     2. It is proper here to consider, 1. by what authority a blockade can
be established; 2. what force is sufficient to constitute a blockade; 3. the
consequences of a violation of the blockade.
     3. - 1. Natural sovereignty confers the right of declaring war, and the
right which nations at war have of destroying or capturing each other's
citizens, subjects or goods, imposes on neutral nations the obligation not
to interfere with the exercise of this right within the rules prescribed by
the law of nations. A declaration of a siege or blockade is an act of
sovereignty, 1 Rob. Rep. 146; but a direct declaration by the sovereign
authority of the besieging belligerent is not always requisite; particularly
when the blockade is on a distant station; for its officers may have power,
either expressly or by implication, to institute such siege or blockade. 6
Rob. R. 367.
     4. - 2. To be sufficient, the blockade must be effective, and made
known. By the convention of the Baltic powers of 1780, and again in 1801,
and by the ordinance of congress of 1781, it is required there should be a
number of vessels stationed near enough to the port to make the entry
apparently dangerous. The government of the United States has, uniformly
insisted, that the blockade should be effective by the presence of a
competent force, stationed and present, at or near the entrance of the port.
1 Kent, Com. 145, and the authorities by him cited; and see 1 Rob. R. 80; 4
Rob. R. 66; 1 Acton's R. 64, 5; and Lord Erskine's speech, 8th March, 1808,
on the orders in council, 10 Cobber's Parl. Debates, 949, 950. But "it is
not an accidental absence of the blockading force, nor the circumstance of
being blown off by wind, (if the suspension and the-reason of the suspension
are known,) that will be sufficient in law to remove a blockade." But
negligence or remissness on the part of the cruisers stationed to maintain
the blockade, may excuse persons, under circumstances, for violating the
blockade. 3 Rob. R. 156 .) 1 Acton's R. 59. To involve a neutral in the
consequences of violating a blockade, it is indispensable that he should
have due notice of it: this information may be communicated to him in two
ways; either actually, by a formal notice from the blockading power, or
constructively by notice to his government, or by the notoriety of the fact.
6 Rob. R. 367; 2 Rob. R. 110; Id. 111, note; Id. 128; 1 Acton's R. 6 1.
     4. - 3. In considering the consequences of the violation of a blockade,
it is proper to take a view of what will amount to such a violation, and,
then, of its effects. As all criminal acts require an intention to commit
them, the party must intend to violate the blockade, or his acts will be
perfectly innocent; but this intention will be judged of by the
circumstances. This violation may be, either, by going into the place
blockaded, or by coming out of it with a cargo laden after the commencement
of the blockade. Also placing himself so near a blockaded port as to be in a
condition to slip in without observation, is a violation of the blockade,
and raises the presumption of a criminal intent. 6 Rob. R. 30, 101, 182; 7
John. R. 47; 1 Edw. R. 202; 4 Cranch, 185. The sailing for a blockaded port,
knowing it to be blockaded, is, it seems, such an act as may charge the
party with a breach of the blockade. 5 Cranch, 335 9 Cranch, 440, 446; 1
Kent, Com. 150. When the ship has contracted guilt by a breach of the
blockade, she may be taken at any time before the end of her voyage, but the
penalty travels no further than the end of her return voyage. 2 Rob. R. 128;
3 Rob. R. 147. When taken, the ship is confiscated; and the cargo is always,
prima facie, implicated in the guilt of the owner or master of the ship and
the burden of rebutting the presumption that the vessel was going in for the
benefit of the cargo, and with the direction of the owners, rests with them.
1 Rob. R. 67, 130 3 Rob. R. 173 4 Rob. R. 93; 1 Edw. It 39. Vide, generally,
2 Bro. Civ. & Adm. Law, 314 Chit. Com. Law, Index, h. t.; Chit. Law of
Nations, 128 to 147; 1 Kent's Com. 143 to 151; Marsh. Ins. Index, h. t.;
Dane's Ab. Index, h. t.; Mann. Com. B. 3, c. 9.