done or occurring in a brief period of time, Advancing with haste or speed; speedy in progression; in quick sequence, characterized by speed; moving with or capable of moving with high speed, noun_ a part of a river where the current is very fast, An extremely fast-moving part of a river, caused by a steep descent in the riverbed, The part of a river where the current moves with great swiftness, but without actual waterfall or cascade; sometimes called whitewater; -- usually used in the plural