"he was held in solitary"

"a lone wolf"
"a lonely existence"
"a man of a solitary disposition"
"a solitary walk"

"solitary bees"

"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"

"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"

"a lonely crossroads"
"a solitary retreat"
"a trail leading to an unfrequented lake"