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]