rapid Definition

rapid
adj

1. Moving, acting or happening quickly; fast.

Thesaurus: fast, quick, speedy, hurried, prompt, brisk, swift, fleet, headlong, precipitate, mercurial; Antonym: leisurely, sluggish.
2. photog.
Requiring short exposure.

noun

1. A part of a river where the water flows quickly, usually over dangerous, sharply descending rocks.

Form: rapids (usually)

Derivative: rapidity
noun

Derivative: rapidly
adverb

Etymology: 17c: from Latin rapidus, from rapere to seize.