Sister Boy 

A feminine, homo-type of a male. Used several times in the movie "Tombstone"

Curly Bill, Ringo and their Cowboy
entourage form a block in the center
Rows while BILLY BREKENRIDGE, Behan's bespectacled, slightly
effeminate little Deputy makes his timid way down the aisle,
looking for a seat midst the off fist-fight and yelling match.
2 cocky young Cowboys, BILLY GROUNDS and ZWING HUNT, call out
to him:

HUNT: "Hey, Sister Boy!"

Sister Boy by Matthew Boyd September 1, 2005

Sisters boy 

A Boy close to his older sister

He always gets so mad when people say hes a sisters boy

Sisters boy by 459395 March 28, 2023

Sisterboy

A boy thatyou know and have the same kind of relationship as a sister or girl with.

I took my sisterboy shopping and we picked out cute matching outfitts ;)

Sisterboy by Sweetyboy, huggs n Kisses July 23, 2010