The Collaborative International Dictionary of English v.0.48:

Invade \In*vade"\, v. i.
   To make an invasion. --Brougham.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Invade \In*vade"\, v. t. [imp. & p. p. Invaded; p. pr. & vb.
   n. Invading.] [L. invadere, invasum; pref. in- in + vadere
   to go, akin to E. wade: cf. OF. invader, F. envahir. See
   Wade.]
   [1913 Webster]
   1. To go into or upon; to pass within the confines of; to
      enter; -- used of forcible or rude ingress. [Obs.]
      [1913 Webster]

            Which becomes a body, and doth then invade
            The state of life, out of the grisly shade.
                                                  --Spenser.
      [1913 Webster]

   2. To enter with hostile intentions; to enter with a view to
      conquest or plunder; to make an irruption into; to attack;
      as, the Romans invaded Great Britain.
      [1913 Webster]

            Such an enemy
            Is risen to invade us.                --Milton.
      [1913 Webster]

   3. To attack; to infringe; to encroach on; to violate; as,
      the king invaded the rights of the people.
      [1913 Webster]

   4. To grow or spread over; to affect injuriously and
      progressively; as, gangrene invades healthy tissue.

   Syn: To attack; assail; encroach upon. See Attack.
        [1913 Webster]

WordNet (r) 3.0 (2006):

invade
    v 1: march aggressively into another's territory by military
         force for the purposes of conquest and occupation; "Hitler
         invaded Poland on September 1, 1939" [syn: invade,
         occupy]
    2: to intrude upon, infringe, encroach on, violate; "This new
       colleague invades my territory"; "The neighbors intrude on
       your privacy" [syn: intrude on, invade, obtrude upon,
       encroach upon]
    3: occupy in large numbers or live on a host; "the Kudzu plant
       infests much of the South and is spreading to the North"
       [syn: invade, overrun, infest]
    4: penetrate or assault, in a harmful or injurious way; "The
       cancer had invaded her lungs"

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "invade":
   adopt, advance upon, appropriate, arrogate, assume, barge in,
   beset, board, break bounds, break in, break in upon, burst in,
   butt in, charge in, come between, crash, crash in, crash the gates,
   crawl with, creep in, creep with, crowd in, cut in, edge in,
   elbow in, encroach, entrench, escalade, foist in, foray,
   go too far, horn in, impinge, impose, impose on, impose upon,
   infest, infiltrate, infringe, inroad, insinuate, interfere,
   interlope, interpose, intervene, intrude, inundate, irrupt,
   know no bounds, make a raid, make an inroad, obtrude, overrun,
   overspread, overstep, overstep the bounds, overswarm, overwhelm,
   plague, play God, press in, pretend to, push in, put on, put upon,
   raid, ravage, rush in, scale, scale the walls, seize, slink in,
   slip in, smash in, sneak in, squeeze in, steal in, storm, storm in,
   swarm, swarm with, take by storm, take over, throng in, thrust in,
   transgress, trench, trespass, usurp, work in, worm in