By the 1930s, "there was no more damning insult than to be called a sissy" and the word was widely used by American football coaches and sports writers to disparage rival teams and encourage ferocious player behavior.
In evolutionary biology, the term cuckold is also applied to males who unwittingly invest parental effort in offspring that are not genetically their own.
Research published in 2015 suggests that the terms are asymmetrical in their power to stigmatize: sissy is almost always pejorative and conveys greater severity, while tomboy rarely causes as much concern but also elicits pressure to conform to normative gender roles.
Sissy (or sis) can also be a relationship nickname formed from sister, given to girls to indicate their role in the family, especially the oldest female sibling.
It can also be applied to girls as a term of affection from friends who are not family members. The Japanese word bishōnen is also a polite term for a man or boy with gentle or feminine attributes.