Rapid

1. (a.) Very swift or quick; moving with celerity; fast; as, a rapid stream; a rapid flight; a rapid motion.
2. (a.) Advancing with haste or speed; speedy in progression; in quick sequence; as, rapid growth; rapid improvement; rapid recurrence; rapid succession.
3. (a.) Quick in execution; as, a rapid penman.
4. (a.) 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.