parenthetical vs parenthetic

parenthetical is a noun but parenthetic is not a noun.

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

As adjectives, parenthetical and parenthetic are synonyms defined as:

parenthetical and parenthetic: qualifying or explaining; placed or as if placed in parentheses

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

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