noun

• (poker slang) A pair of jacks.
• (UK, rhyming slang) Heroin tablets (from "jacks and jills" = pills)
• (games) A children's game involving picking up objects; knucklebones; jackstones.
• A surname originating as a patronymic derived from Jack.
• (slang, now chiefly Ireland) Alternative form of jakes: an outhouse or lavatory. [.]](now chiefly Ireland) A place to urinate and defecate: an outhouse or lavatory.]