hit (someone or something) very hard, especially to knock unconscious. Possibly from an old sailors' game "building the galleass" (galleass: a wargalley) where a new sailor (the victim) would be hit in the face with a mop dipped in a slop bucket knocking him "galleass" (to the deck of the galleas). —AcademyLevel I Glossary - Approved November 1990