solitary
/ˈsä-lə-ˌter-ē/
adjective
being, living, or going alone or without companions
saddened by isolation
unfrequented, desolate
noun
one who lives or seeks to live a solitary life : recluse
solitary confinement in prison
noun
the state of being kept alone in a prison cell away from other prisoners
He spent three months in solitary confinement.