rapid (adj.)

1630s, "moving quickly," from French rapide (17c.) and directly from Latin rapidus "hasty, swift, rapid; snatching; fierce, impetuous," from rapere "hurry away, carry off, seize, plunder," from PIE root *rep- "to snatch" (source also of Greek ereptomai "devour," harpazein "snatch away," Lithuanian raplės "tongs"). Meaning "happening in a short time" is from 1780. Related: Rapidly; rapidness. Rapid-transit first attested 1852, in reference to street railways; rapid eye movement is from 1906.

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Definitions of rapid from WordNet
rapid (adj.)
done or occurring in a brief period of time;
a rapid rise through the ranks
rapid (adj.)
characterized by speed; moving with or capable of moving with high speed;
a rapid movement
Synonyms: speedy
rapid (n.)
a part of a river where the current is very fast;