The Collaborative International Dictionary of English v.0.48:

Succumb \Suc*cumb"\, v. t. [imp. & p. p. Succumbed; p. pr. &
   vb. n. Succumbing.] [L. succumbere; sub under + cumbere (in
   comp.), akin to cubare to lie down. See Incumbent,
   Cubit.]
   To yield; to submit; to give up unresistingly; as, to succumb
   under calamities; to succumb to disease.
   [1913 Webster]

WordNet (r) 3.0 (2006):

succumb
    v 1: consent reluctantly [syn: yield, give in, succumb,
         knuckle under, buckle under]
    2: be fatally overwhelmed [syn: succumb, yield] [ant: come
       through, make it, pull round, pull through, survive]

Moby Thesaurus II by Grady Ward, 1.0:

122 Moby Thesaurus words for "succumb":
   abandon, accede, accept, acquiesce, assent, be agreeable,
   be done for, be lost, be no more, bite the dust, black out, blow,
   bow, bow to, break down, burn out, capitulate, cash in, cave,
   cease, cease to be, cease to live, collapse, come to naught,
   come to nothing, comply, conk out, consent, crack up, decease,
   defer, defer to, demise, depart, depart this life, die, disappear,
   droop, drop, end, expire, face the music, fade away, faint, fall,
   fall asleep, fall senseless, fatigue, flag, gasp, get tired,
   give out, give up, give way, give way to, go, go along with,
   go down, go out, go under, gray out, grow weary, have enough, jade,
   keel over, knock under, knuckle, knuckle down, knuckle under,
   knuckle under to, lick the dust, live with it, lose, lose out,
   lose the day, not resist, obey, pant, part, pass, pass away,
   pass on, pass out, pass over, peg out, perish, peter out, play out,
   poop out, puff, puff and blow, put off mortality, quit this world,
   relent, relinquish, resign, return to dust, run down, run out,
   say uncle, sink, stop breathing, submit, submit to, succumb to,
   surrender, swallow it, swallow the pill, swoon, take, take it,
   take the count, tire, tumble, up and die, vanish, weary, wheeze,
   wilt, yield, yield the ghost, yield to