rainbow troutn. A freshwater or anadromous food and game fish (Oncorhynchus mykiss) native to western North America, having a reddish longitudinal band and black spots.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.rainbow trout n (Animals) 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 and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014rain?bow trout` n. a plump trout, Salmo gairdneri, native to W North American streams, having vertical reddish stripes on a black-speckled, green-to-turquoise body. [1880?85, Amer.] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.