parenthetical expression vs parenthetical

parenthetical expression and parenthetical both are nouns.

Word	Noun	Adjective	Verb	Adverb
parenthetical expression	Yes	No	No	No
parenthetical	Yes	Yes	No	No

As nouns, parenthetical expression and parenthetical are synonyms defined as:

parenthetical expression and parenthetical: an expression in parentheses

parenthetical expression (noun)	parenthetical (noun)
an expression in parentheses	an expression in parentheses

parenthetical expression (adjective)	parenthetical (adjective)
	qualifying or explaining; placed or as if placed in parentheses