ro·ta·ry / ˈrōtərē/ • adj. (of motion) revolving around a center or axis; rotational: a rotary motion. ∎ (of a thing) acting by means of rotation, esp. (of a machine) operating through the rotation of some part: a rotary mower.• n. (pl. -ries) 1. a rotary machine, engine, or device. 2. a traffic circle.