Avon vs Upper Avon

Avon and Upper Avon both are nouns.

Word	Noun	Adjective	Verb	Adverb
Avon	Yes	No	No	No
Upper Avon	Yes	No	No	No

As nouns, Avon and Upper Avon are synonyms defined as:

Avon and Upper Avon: a river in central England that flows through Stratford-on-Avon and empties into the Severn

Other synonyms of Avon include River Avon, Upper Avon River.

Avon (noun)	Upper Avon (noun)
a county in southwestern England, named after the river Avon	a river in central England that flows through Stratford-on-Avon and empties into the Severn
a river in central England that flows through Stratford-on-Avon and empties into the Severn
a river in southwestern England rising in Gloucestershire and flowing through Bristol to empty into the estuary of the Severn