corker n.

"unanswerable fact or argument," 1837, slang, something that "settles" a debate, discussion, conflict, etc.; hence "something astonishing" (1880s). Probably an agent noun from cork (v.) on the notion is of putting a cork in a bottle as an act of finality. Corker in the literal sense of "one who or that which corks" is from 1880.