The word believe can have the past participle (believed) as an adjective, but it has no adverb form. The present participle has the rarely seen adverb form believingly. There is a related adjective believable which has the adverb form believably.
I believe the adjective form of illustrate is illustrational.SSH
The adjective form of concept is conceptual.The adjective form of conception is conceptional.
The adjective form for the pronoun they is their.
The Adjective form of Pathologist is Pathological.
The adjective form of concept is conceptual.The adjective form of conception is conceptional.
The adjective form of improve is "improved."
The word 'opposite' is a noun form, a word for something that is contrary of another.Example: They believe that these measures will solve the problem but I believe the opposite.The noun form of the adjective 'opposite' is oppositeness.
The word convinced can be an adjective and a verb. The adjective form means to be in a state of believing. The verb form is the past tense of the verb "convince" which means to make someone believe something.
adjective form of pass.
The adjective form is decisive.
The adjective form is patient.