washing soda vs soda ash

washing soda and soda ash both are nouns.

Word	Noun	Adjective	Verb	Adverb
washing soda	Yes	No	No	No
soda ash	Yes	No	No	No

As nouns, washing soda and soda ash are synonyms defined as:

washing soda and soda ash: a sodium salt of carbonic acid; used in making soap powders and glass and paper

Other synonyms of washing soda include sal soda, soda, sodium carbonate.

washing soda (noun)	soda ash (noun)
a sodium salt of carbonic acid; used in making soap powders and glass and paper	a sodium salt of carbonic acid; used in making soap powders and glass and paper