obsession vs obsessional

obsession is a noun but obsessional is not a noun.

Word	Noun	Adjective	Verb	Adverb
obsession	Yes	No	No	No
obsessional	No	Yes	No	No

obsession (noun)	obsessional (noun)
an unhealthy and compulsive preoccupation with something or someone
an irrational motive for performing trivial or repetitive actions, even against your will

obsession (adjective)	obsessional (adjective)
	characterized by or constituting an obsession