Rapid :: Rapid (a.) Very swift or quick; moving with celerity; fast; as, a rapid stream; a rapid flight; a rapid motion..
Rapid :: Rapid (a.) Advancing with haste or speed; speedy in progression; in quick sequence; as, rapid growth; rapid improvement; rapid recurrence; rapid succession..
Rapid :: Rapid (a.) Quick in execution; as, a rapid penman..
Rapid :: Rapid (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..
Rapidity :: Rapidity (n.) The quality or state of being rapid; swiftness; celerity; velocity; as, the rapidity of a current; rapidity of speech; rapidity of growth or improvement..