bird

Bird comes from Middle English bird/brid, from Old English bridd, meaning a chick, fledgling, or chicken — a term of uncertain origin.

Old English had a separate word, fugol (the ancestor of "fowl"), for flying birds in general, while bridd was reserved for young or flightless ones. Starting in the 14th century, bird gradually took over as the everyday word, pushing fowl toward its narrower modern sense.

The word fowl was once the general term for birds in Old English, while bird described only the young — the two swapped places in everyday use over time.