deer

From Middle English der, deer ("animal, deer"), from Old English dēor ("animal"), from Proto-West Germanic *deuʀ, from Proto-Germanic *deuzą, ultimately from Proto-Indo-European *dʰewsóm ("living thing"), itself from *dʰéws ("breath").

The word narrowed over time: it started out meaning "animal" in general in Old English, and eventually settled into naming one particular creature, the deer, in modern English.

It's cognate with German Tier and Dutch dier, both of which still mean "animal" broadly — showing that English narrowed a word other Germanic languages kept general. The deep root traces back to a word for "breath," much as Latin animal comes from anima, "breath, spirit."