Webster's Revised Unabridged Dictionary · 1913

Rapid

Rapid (rap"id) , adjective

[Latin rapidus, from rapere to seize and carry off, to snatch or hurry away; perhaps akin to Greek 'arpa`zein: compare French rapide. Compare Harpy, Ravish.]

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.

Rapid (rap"idz) , noun

[Compare French rapide. See Rapid, a.]

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; as, the Lachine rapids in the St. Lawrence. For boaters on the river, it is a place that can be hazardous, with danger of capsizing or crashing into large rocks.
Row, brothers, row, the stream runs fast, The rapids are near, and the daylight's past. — Moore

Also: Rapids