adv. Naut. [f. as prec. + -s of adverbial genitive.] = prec. B.
a. 1625. Nomenclator Navalis (Harl. MS. 2301), s.v., Anie thing that is done or lies acrosse ye Shipp from one side to thother wee saie that it lies thwart ships.
1718. Steele, Fish Pool, 175. The depth of the arch of the deck thwartships is 4 inches.