heron

Heron comes from Middle English heroun, from Anglo-Norman heiron, from Medieval Latin hairō, tracing back through Frankish and Proto-West Germanic *hraigrō to Proto-Germanic *haigrô. That Germanic root is imitative, built from a Proto-Indo-European base *(s)kreik-/*(s)kreig- meaning 'to screech, creak.'

The word's sound shifted along the way — the Germanic form *haigrô is a dissimilation of an earlier *hraigrô, which survives more directly in Old English hrāgra, Dutch reiger, and German Reiher.

Egret comes from the same Germanic root, making these two long-legged wading birds etymological cousins. Welsh crëyr and Ancient Greek krízō, meaning 'to creak, screech,' point back to the same screeching origin.