WordNet (r) 3.0 (2006):

sissy
    adj 1: having unsuitable feminine qualities [syn: effeminate,
           emasculate, epicene, cissy, sissified,
           sissyish, sissy]
    n 1: a timid man or boy considered childish or unassertive [syn:
         sissy, pantywaist, pansy, milksop, Milquetoast]