A girl or woman who only is attracted to girls. Calling a woman or girl a Femmesy implies that they are or have been sexually and/or emotionally involved with another female. A synonym for Lesbian.
Girl 1: "Did you see her check Catalina out?"
Girl 2: "Yeah, I think she's another Femmesy."
A proud Femmesy: "Yes, I'm a Femmesy b*tch! Is that a problem?"
A closeted Femmesy: "Nah Angie, it's totally fine with me."
Boy 1: "Dude, she's a lesbian, a femmesy, chillin' on the rainbow. She doesn't like you."
Boy 2: "Darn it! I always fall for the chicks that like chicks."