apposition vs appositional

apposition is a noun but appositional is not a noun.

Word	Noun	Adjective	Verb	Adverb
apposition	Yes	No	No	No
appositional	No	Yes	No	No

apposition (noun)	appositional (noun)
the act of positioning close together (or side by side)
(biology) growth in the thickness of a cell wall by the deposit of successive layers of material
a grammatical relation between a word and a noun phrase that follows

apposition (adjective)	appositional (adjective)
	relating to or being in apposition