"swift current in a river where the channel is descending," 1765, from French rapides (see rapid); applied by French voyagers to rough, swift-flowing reaches in North American rivers.
Entries linking to rapids
rapid adj.
1630s, "moving or doing quickly, capable of great speed," from French rapide (17c.) and directly from Latin rapidus "hasty, swift; 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, coming quickly into existence" is from 1780. Related: Rapidly; rapidness. Rapid-fire (adj.) 1890 in reference to guns, figurative or transferred use by 1900; the noun phrase is by 1836. Rapid-transit first attested 1852, in reference to street railways; rapid eye movement, associated with a certain phase of sleep, is from 1906.