0 a boy who other boys dislike and laugh at because they think he is weak or interested in activities girls usually like, or a person who is weak and cowardly (= not brave):
Kevin is such a sissy.
[ as form of address ] Can't you climb that tree, you big sissy?
1 (of a boy) weak and not brave, or interested in activities girls usually like:
2 a boy who seems to be easily frightened and not brave, or who is not interested in things boys usually like:
Dancing was for sissies when I was a kid.
UK A lad that wore pyjamas was considered to be a bit of a sissy type of a lad.
These stories are cool, tough, and outrageous, and prove that girls don't have to be sissy.