The Collaborative International Dictionary of English v.0.48:

Forgo \For*go"\, v. t. [imp. Forwent; p. p. Forgone; p. pr.
   & vb. n. Forgoing.] [OE. forgan, forgon, forgoon, AS.
   forg[=a]n, prop., to go past, hence, to abstain from; pref.
   for- + g[=a]n to go; akin to G. vergehen to pass away, to
   transgress. See Go, v. i.]
   1. To pass by; to leave. See 1st Forego.
      [1913 Webster]

            For sith [since] I shall forgoon my liberty
            At your request.                      --Chaucer.
      [1913 Webster]

            And four [days] since Florimell the court forwent.
                                                  --Spenser.
      [1913 Webster]

   2. to abstain from; to do without; to refrain from; to
      renounce; -- said of a thing already enjoyed, or of one
      within reach, or anticipated. See 1st forego, 2.
      [PJC]

   Note: This word in spelling has been confused with, and
         almost superseded by, forego to go before.
         Etymologically the form forgo is correct.
         [1913 Webster]

WordNet (r) 3.0 (2006):

forgo
    v 1: do without or cease to hold or adhere to; "We are
         dispensing with formalities"; "relinquish the old ideas"
         [syn: waive, relinquish, forgo, forego,
         foreswear, dispense with]
    2: be earlier in time; go back further; "Stone tools precede
       bronze tools" [syn: predate, precede, forego, forgo,
       antecede, antedate] [ant: follow, postdate]
    3: lose (s.th.) or lose the right to (s.th.) by some error,
       offense, or crime; "you've forfeited your right to name your
       successor"; "forfeited property" [syn: forfeit, give up,
       throw overboard, waive, forgo, forego] [ant:
       arrogate, claim, lay claim]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "forgo":
   abandon, abdicate, abjure, abstain, abstain from,
   acknowledge defeat, avoid, cease, cede, cry quits, desist from,
   disgorge, dispense with, dispose of, do without, drop, dump,
   eliminate, eschew, forbear, forsake, forswear, get along without,
   get rid of, give away, give over, give up, hand over,
   have done with, hold, hold aloof from, hold back, hold off,
   keep back, keep from, keep in hand, kiss good-bye, lay down,
   leave alone, leave off, leave out, let alone, let go by,
   make a sacrifice, never touch, not touch, not use, omit, part with,
   pass up, quitclaim, recant, refrain, refrain from, relinquish,
   render up, renounce, reserve, resign, retract, sacrifice, save,
   shun, spare, stand aloof from, surrender, swear off, throw up,
   turn down, vacate, waive, withhold, yield