The Collaborative International Dictionary of English v.0.48:

Weak-hearted \Weak"-heart`ed\, a.
   Having little courage; of feeble spirit; dispirited;
   faint-hearted. "Weak-hearted enemies." --Shak.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "weakhearted":
   afraid, chicken, chickenhearted, coward, cowardly, cowed, daunted,
   dismayed, fainthearted, fearful, funking, funky, henhearted,
   intimidated, lily-livered, milk-livered, milksoppish, milksoppy,
   mousy, overtimid, overtimorous, panic-prone, panicky,
   pigeonhearted, rabbity, sissified, sissy, soft, timid, timorous,
   unmanly, unmanned, weak, weak-kneed, white-livered, yellow