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guinea pig

American  

noun

  1. a short-eared, tailless rodent of the genus Cavia, usually white, black, and tawny, commonly regarded as the domesticated form of one of the South American wild species of cavy: often used in scientific experiments or kept as a pet.

  2. Informal. the subject of any sort of experiment.

    I've volunteered as a guinea pig in several clinical trials.
guinea pig British  

noun

  1. a domesticated cavy, probably descended from Cavia porcellus, commonly kept as a pet and used in scientific experiments

  2. a person or thing used for experimentation

"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

Etymology

Origin of guinea pig

First recorded in 1655–65

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.