A small animal or creature, especially a wild or domesticated four-legged animal like a squirrel or raccoon.
From 'creature,' simplified and made informal through American English dialect. The word became especially popular in the 1800s-1900s in American rural and frontier language.
Critter is such a distinctly American word that it's rarely used in British English! Animal behaviorists study wild critters by tracking them with GPS tags and cameras, discovering that animals like raccoons are surprisingly intelligent problem-solvers and can remember how to open complex locks.
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