The Collaborative International Dictionary of English v.0.48:

Forbid \For*bid"\, v. i.
   To utter a prohibition; to prevent; to hinder. "I did not or
   forbid." --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Forbid \For*bid"\ (f[o^]r*b[i^]d"), v. t. [imp. Forbade
   (f[o^]r*b[a^]d"); p. p. Forbidden (f[o^]r*b[i^]d"d'n)
   (Forbid, [Obs.]); p. pr. & vb. n. Forbidding
   (f[o^]r*b[i^]d"d[i^]ng).] [OE. forbeden, AS. forbe['o]dan;
   pref. for- + be['o]dan to bid; akin to D. verbieden, G.
   verbieten, Icel. fyrirbj[=o][eth]a, forbo[eth]a, Sw.
   f["o]rbjuda, Dan. forbyde. See Bid, v. t.]
   1. To command against, or contrary to; to prohibit; to
      interdict.
      [1913 Webster]

            More than I have said . . .
            The leisure and enforcement of the time
            Forbids to dwell upon.                --Shak.
      [1913 Webster]

   2. To deny, exclude from, or warn off, by express command; to
      command not to enter.
      [1913 Webster]

            Have I not forbid her my house?       --Shak.
      [1913 Webster]

   3. To oppose, hinder, or prevent, as if by an effectual
      command; as, an impassable river forbids the approach of
      the army.
      [1913 Webster]

            A blaze of glory that forbids the sight. --Dryden.
      [1913 Webster]

   4. To accurse; to blast. [Obs.]
      [1913 Webster]

            He shall live a man forbid.           --Shak.
      [1913 Webster]

   5. To defy; to challenge. [Obs.] --L. Andrews.

   Syn: To prohibit; interdict; hinder; preclude; withhold;
        restrain; prevent. See Prohibit.
        [1913 Webster]

WordNet (r) 3.0 (2006):

forbid
    v 1: command against; "I forbid you to call me late at night";
         "Mother vetoed the trip to the chocolate store"; "Dad nixed
         our plans" [syn: forbid, prohibit, interdict,
         proscribe, veto, disallow, nix] [ant: allow,
         countenance, let, permit]
    2: keep from happening or arising; make impossible; "My sense of
       tact forbids an honest answer"; "Your role in the projects
       precludes your involvement in the competitive project" [syn:
       prevent, forestall, foreclose, preclude, forbid]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "forbid":
   anticipate, avert, ban, bar, block, check, curb, debar, deflect,
   deny, deter, disallow, discourage, dishearten, embargo, enjoin,
   estop, exclude, exclude from, fend, fend off, foreclose, forestall,
   halt, help, hinder, impede, inhibit, interdict, keep from,
   keep off, obstruct, obviate, outlaw, preclude, prevent, prohibit,
   proscribe, refuse, reject, repel, repress, restrain, rule out,
   save, say no to, shut out, stave off, stop, suppress, taboo,
   turn aside, veto, ward off