The Collaborative International Dictionary of English v.0.48:

Timorous \Tim"or*ous\, a. [LL. timorosus, from L. timor fear;
   akin to timere to fear. See Timid.]
   1. Fearful of danger; timid; deficient in courage. --Shak.
      [1913 Webster]

   2. Indicating, or caused by, fear; as, timorous doubts. "The
      timorous apostasy of chuchmen." --Milman.
      [1913 Webster] -- Tim"or*ous*ly, adv. --
      Tim"or*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

timorous
    adj 1: timid by nature or revealing timidity; "timorous little
           mouse"; "in a timorous tone"; "cast fearful glances at
           the large dog" [syn: fearful, timorous, trepid]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "timorous":
   afraid, bashful, chicken, chickenhearted, confused, conscious,
   coward, cowardly, cowed, coy, daunted, demure, diffident, dismayed,
   fainthearted, fearful, fearing, fearsome, funking, funky, goosy,
   henhearted, in fear, inarticulate, intimidated, jumpy,
   lily-livered, milk-livered, milksoppish, milksoppy, mousy, nervous,
   overtimid, overtimorous, panic-prone, panicky, pigeonhearted,
   quailing, quivering, rabbity, recoiling, scary, self-conscious,
   shaky, shamefaced, shamefast, shivering, shivery, shrinking,
   shuddering, shy, sissified, sissy, skittery, skittish, soft,
   stammering, startlish, timid, trembling, tremulous, trepidant,
   trigger-happy, undaring, unmanly, unmanned, weak, weak-kneed,
   weakhearted, white-livered, yellow