1. An insulting word for a boy or a man who appears to do things like girls or women: People laughed at Monroe and called him a sissy because he wouldn't play football.
2. Anyone who is regarded as being overly timid, weak, fearful, or cowardly: Pete was called a sissy because he was afraid to touch a little frog.
3. Etymology: from about 1846, "sister", an extended form of sis that refers to a male as being an "effeminate person".

A reference to someone or something that is considered unmasculine or not manly: Dennis wouldn't play golf because he thought it was a sissy sport.