The Collaborative International Dictionary of English v.0.48:

Milquetoast \Milquetoast\ n. [From Caspar Milquetoast, a
   character in a cartoon strip by H. T. Webster, The Timid Soul
   (1935).]
   a timid, unassertive man or boy fearful of confrontation and
   easily manipulated and dominated.

   Syn: sissy, pantywaist, pansy, milksop.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Milquetoast
    n 1: a timid man or boy considered childish or unassertive [syn:
         sissy, pantywaist, pansy, milksop, Milquetoast]