Chiefly Geometry. An angle of ninety degrees; spec. one formed by two perpendicular lines, as in the corner of a square or in a quartered circle.

†(a) = right angle, n. 1 (obsolete); (b) a corner formed by the meeting of two or more planes which are perpendicular to each other (now rare).

A right angle. In later use esp. in at rectangles (cf. at right angles at right angle, n. 2). Cf. rect angle n. at rect, adj. compounds. Now rare.

Astronomy. The right angle between the sight lines of two celestial objects in quadrature. Obsolete. rare.

straight angle. A right angle. Obsolete.