suspect vs questionable

suspect is a noun but questionable is not a noun.

Word	Noun	Adjective	Verb	Adverb
suspect	Yes	Yes	Yes	No
questionable	No	Yes	No	No

suspect (noun)	questionable (noun)
someone who is under suspicion
a person or institution against whom an action is brought in a court of law; the person being sued or accused

suspect (adjective)	questionable (adjective)
not as expected	subject to question
	able to be refuted

suspect (verb)	questionable (verb)
regard as untrustworthy; regard with suspicion; have no faith or confidence in
imagine to be the case or true or probable
hold in suspicion; believe to be guilty