The Collaborative International Dictionary of English v.0.48:

Relinquish \Re*lin"quish\ (-kw?sh), v. t. [imp. & p. p.
   Relinquished (-kw?sht); p. pr. & vb. n. Relinquishing.]
   [OF. relinquir, L. relinquere to leave behind; pref. re- re +
   linquere to leave. See Loan, and cf. Relic, Relict.]
   [1913 Webster]
   1. To withdraw from; to leave behind; to desist from; to
      abandon; to quit; as, to relinquish a pursuit.
      [1913 Webster]

            We ought to relinquish such rites.    --Hooker.
      [1913 Webster]

            They placed Irish tenants upon the lands
            relinquished by the English.          --Sir J.
                                                  Davies.
      [1913 Webster]

   2. To give up; to renounce a claim to; resign; as, to
      relinquish a debt.
      [1913 Webster]

   Syn: To resign; leave; quit; forsake; abandon; desert;
        renounce; forb?ar; forego. See Resign.
        [1913 Webster]

WordNet (r) 3.0 (2006):

relinquish
    v 1: part with a possession or right; "I am relinquishing my
         bedroom to the long-term house guest"; "resign a claim to
         the throne" [syn: release, relinquish, resign,
         free, give up]
    2: 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]
    3: turn away from; give up; "I am foreswearing women forever"
       [syn: foreswear, renounce, quit, relinquish]
    4: release, as from one's grip; "Let go of the door handle,
       please!"; "relinquish your grip on the rope--you won't fall"
       [syn: let go of, let go, release, relinquish] [ant:
       hold, take hold]

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "relinquish":
   abandon, abdicate, abjure, abnegate, abort, acknowledge defeat,
   be pensioned, be superannuated, beg a truce, belay, cancel,
   capitulate, cast, cease, cede, come off, come to terms, cry pax,
   cry quits, cut it out, cut out, demit, desert, desist, desist from,
   discard, discontinue, disgorge, dispense with, dispose of, disuse,
   do without, drop, drop it, dump, end, forbear, forgo, forsake,
   forswear, free, get along without, get rid of, give away,
   give over, give up, halt, hand over, have done with, hold,
   implore mercy, kiss good-bye, knock it off, lay aside, lay down,
   lay off, leave, leave off, let go, loose, make a sacrifice,
   nol-pros, not pursue with, part with, pension off,
   pray for quarter, put behind one, quit, quitclaim, recant, refrain,
   release, render up, renounce, renounce the throne, resign, retire,
   retire from office, retract, sacrifice, say uncle, scrub, shed,
   spare, stand aside, stand down, stay, step aside, stop,
   superannuate, surrender, swear off, terminate, throw up, turn up,
   unloose, vacate, waive, withdraw from, yield, yield the palm