Rapid

Part of speech: noun (n.)

The part of a river where the current moves with great swiftness, but without actual waterfall or cascade; -- usually in the plural; as, the Lachine rapids in the St. Lawrence. Row, brothers, row the stream runs fast, The rapids are near, and the daylight's past. Moore.

Part of speech: adjective (a.)

1. Very swift or quick; moving with celerity; fast; as, a rapid stream; a rapid flight; a rapid motion. Ascend my chariot; guide the rapid wheels. Milton.

2. Advancing with haste or speed; speedy in progression; in quick sequence; as, rapid growth; rapid improvement; rapid recurrence; rapid succession.

3. Quick in execution; as, a rapid penman.