Jill Share definition Flag A slang word for female masturbation. As opposed to a male "Jack off", A woman is "Jill off". Shiela said she's going home to study, but she goes home everyday after school to jill off Jill by KittyWithKlaws February 19, 2009 0 0 Get merch Get the Jill mug. Buy Now — $32.95 See more merch