19. (colloquial).—A male: as in the compounds Jack-hare, Jack-crow,
Jack-ass, Jack-rabbit, etc.
1563. Appius & Virginius [Dodsley, Old Plays (1874), iv. 151]. A
gentleman?—nay, a Jack-herring.
1894. De Somerville & Ross, The Real Charlotte, i. 210. And I don’t
care a Jack-rat what he thought, or what you think either.