guinea pig

noun

1

: a small stout-bodied short-eared tailless domesticated rodent (Cavia porcellus) of South American origin often kept as a pet and widely used in biological research

called also cavy

2

: a subject of research, experimentation, or testing

Examples of guinea pig in a Sentence

He volunteered to act as a guinea pig in the experiment.

Recent Examples on the Web

Much of his work involved serving as a guinea pig for medical experiments investigating how his naturally aging body reacted to being in space. —Jeffrey Kluger, Time, 31 Oct. 2025

Like a legless guinea pig or an oversized hamster with no mouth or ears, and beady eyes (stay with me, here). —Brenna Ehrlich, Rolling Stone, 30 Oct. 2025

Pets and backyard animals such as birds, hedgehogs, turtles, guinea pigs and bearded dragons can also carry Salmonella. —Tanya Lewis, Scientific American, 24 Oct. 2025

The farm is home to goats, Holstein cows, potbellied and kune kune pigs, donkeys, sheep, rabbits, llamas, alpacas, guinea fowl, guinea pigs, geese, chickens, a Shetland pony, and a Shire horse. —Rachel Raposas, PEOPLE, 23 Oct. 2025

Word History

First Known Use

1664, in the meaning defined at sense 1

Rhymes for guinea pig

• whirligig
• big
• brig
• brigg
• dig
• fig
• gig
• jig
• mig
• prig
• rig
• sprig

Kids Definition

guinea pig

noun

1

: a small stocky rodent with short ears and a very short tail that is often kept as a pet and is used in biological research

2

: a person or thing experimented on

Medical Definition

guinea pig

noun

guin·​ea pig ˈgin-ē-ˌ 

: a small stout-bodied short-eared nearly tailless domesticated rodent of the genus Cavia (C. cobaya) often kept as a pet and widely used in biological research

called also cavy