pocket

English pocket comes from Middle English pocket ("bag, sack"), from Anglo-Norman poket, a diminutive of poke or poque ("bag, sack"), itself from Frankish *pokō ("pouch"), from Proto-Germanic *puhô ("bag; pouch"), traced back to a Proto-Indo-European root meaning "to blow, swell."

The word began as a small, separate bag or sack, and the diminutive ending marked it as a little one — a pouch small enough to carry, eventually the small sewn-in compartment we know today.

Pocket is a doublet of pochette, and it's cognate with Old English pocca or pohha ("poke, pouch, pocket, bag") and Old Norse poki ("bag, pocket") — all descending from that same Germanic root for a swelling bag.