very swift or quick; moving with celerity; fast; as, a rapid stream; a rapid flight; a rapid motion.-advancing with haste or speed; speedy in progression; in quick sequence; as, rapid growth; rapid improvement; rapid recurrence; rapid succession.-quick in execution; as, a rapid penman.-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.