Nouns

(n)solitary confinement, solitaryconfinement of a prisoner in isolation from other prisoners“he was held in solitary”
(n)hermit, recluse, solitary, solitudinarian, troglodyteone who lives in solitude

Adjectives

(s)lone, lonely, solitarycharacterized by or preferring solitude“a lone wolf”, “a lonely existence”, “a man of a solitary disposition”, “a solitary walk”
(s)nongregarious, nonsocial, solitaryof plants and animals; not growing or living in groups or colonies“solitary bees”
(s)alone, lone, lonely, solitarylacking companions or companionship“he was alone when we met him”, “she is alone much of the time”, “the lone skier on the mountain”, “a lonely fisherman stood on a tuft of gravel”, “a lonely soul”, “a solitary traveler”
(s)lone, lonesome, only, sole, solitarybeing the only one; single and isolated from others“the lone doctor in the entire county”, “a lonesome pine”, “an only child”, “the sole heir”, “the sole example”, “a solitary instance of cowardice”, “a solitary speck in the sky”
(s)lonely, solitary, unfrequenteddevoid of creatures“a lonely crossroads”, “a solitary retreat”, “a trail leading to an unfrequented lake”