a trout, Salmo gairdnerii, native in the coastal waters and streams from Baja California to Alaska, used as a food and game fish.
Origin of rainbow trout
An Americanism dating back to 1880–85
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British Dictionary definitions for rainbow trout
a freshwater trout of North American origin, Salmo gairdneri, having a body marked with many black spots and two longitudinal red stripes
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012