1. [n]  a county in southwestern England
2. [n]  a river in central England that flows through Stratford-on-Avon and empties into the Severn
3. [n]  a river in southwestern England rising in Gloucestershire and flowing through Bristol to empty into the estuary of the Severn

AVON is a 4 letter word that starts with A.

A dataflow language.

["AVON: A Dataflow Language", A. Deb, ICS 87, Second Intl Conf on Supercomputing, v.3, pp.9-19, ISI 1987].