solitary vs unfrequented

solitary is a noun but unfrequented is not a noun.

Word	Noun	Adjective	Verb	Adverb
solitary	Yes	Yes	No	No
unfrequented	No	Yes	No	No

As adjectives, solitary and unfrequented are synonyms defined as:

Other synonyms of solitary include lonely.

solitary (noun)	unfrequented (noun)
one who lives in solitude
confinement of a prisoner in isolation from other prisoners

solitary (adjective)	unfrequented (adjective)
being the only one; single and isolated from others	devoid of creatures
lacking companions or companionship
of plants and animals; not growing or living in groups or colonies
devoid of creatures
characterized by or preferring solitude