River Severn vs Severn River

River Severn and Severn River both are nouns.

Word	Noun	Adjective	Verb	Adverb
River Severn	Yes	No	No	No
Severn River	Yes	No	No	No

As nouns, River Severn and Severn River are synonyms defined as:

River Severn and Severn River: a river in England and Wales flowing into the Bristol Channel; the longest river in Great Britain

Other synonyms of River Severn include Severn.

River Severn (noun)	Severn River (noun)
a river in England and Wales flowing into the Bristol Channel; the longest river in Great Britain	a river in England and Wales flowing into the Bristol Channel; the longest river in Great Britain
	a river in Ontario that flows northeast into Hudson Bay