As an adjective, rapid means happening or moving very quickly. As a noun, “rapids” are sections of a river where the water flows fast and roughly over rocks.
It comes from Latin “rapidus,” meaning “seizing, rushing, swift,” from “rapere,” meaning “to seize or snatch.” English took it through French in the 17th century.
“Rapid” is related to words like “rape” and “raptor,” all originally about seizing or snatching quickly. The idea of speed is so strong in this family of words that we now mostly feel the quickness, not the grabbing, in “rapid.”
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