Synonyms for Sissy (same or very similar meaning)
WordNet sense 1 (a timid man or boy considered childish or unassertive):
milksop, milquetoast, pansy, pantywaistWordNet sense 2 (having unsuitable feminine qualities):
effeminate, emasculate, sissified, epicene, cissy, sissyishWordNet sense 3 (not possessing qualities befitting a man):
unmanly, unmanful, unmanlikeFrom the ODE community, based on WordNetadd/edit