(nautical) A boat, used in competitive rowing, having four rowers, each with a single oar / (rowing, especially in plural) A race in which such craft participate

Alternative spelling of on all fours

(physics) A four-vector that describes the change in a particle's four-momentum over time.

(physics) A generalization of momentum in four-dimensional spacetime.

(physics) A four-vector that describes the change in a particle's four-velocity over time

(physics) A generalization of velocity in four-dimensional spacetime

Alternative spelling of foursquare

plural of four-poster

(attributive, of a bed) Having four vertical columns, one in each corner, that support a tester, so that curtains can be hung to exclude draughts from the sleeper.

A four-poster bed, which has four high posts, one at each corner, supporting a canopy.