Meaning

adverb at right angles to the center line of a ship

adverb at an oblique angle

originFrom Late Middle English athwert, athirt, from a- (prefix meaning ‘in the direction of, toward’) + thwert (“crosswise; (cooking) across the grain”, adverb). Thwert is derived from thwert (“crosswise, transverse; counter, opposing; contrary, obstinate, stubborn”, adjective), borrowed from Old Norse þvert (“across, athwart”), originally the neuter form of þverr (“across, transverse”), from…

Etymology from Wiktionary, CC BY-SA 3.0