athwart

Athwart is a preposition and adverb in English meaning across or from side to side; it denotes a direction that is perpendicular to the main length of something, such as a ship, beam, or structure. The term comes from Middle English, evolving from a word meaning crosswise or across; it has long been established in nautical and architectural language, while largely falling out of everyday use.

In nautical contexts, athwart describes movement, components, or forces oriented perpendicular to a vessel's fore‑aft axis. An athwartship beam runs across the ship's width; the adjective athwartships or the compound form athwartship is often used in technical descriptions to specify crosswise orientation or loads acting across the hull.

Outside maritime usage, athwart appears in architectural and mechanical descriptions to indicate crosswise placement, such as elements laid athwart the span of a bridge or the deck.

Today, athwart is considered formal or archaic outside specialized fields, with across or crosswise as common synonyms. The related term athwartship remains standard in naval architecture and historical texts.