From Longman Dictionary of Contemporary Englishguinea pigˈguinea pig noun [countable] 1 HBAa small furry animal with short ears and no tail, which is often kept as a pet2 TEST/EXPERIMENTsomeone who is used in a scientific test to see how successful or safe a new product, system etc is
Examples from the Corpus
guinea pig• My guests are guinea pigs for all the new dishes I try out.Origin guinea pig (1600-1700) Guinea, probably by mistake for Guiana, earlier name of Guyana 