WordNet sense 1 (lacking companions or companionship):

lone, lonely, solitary

WordNet sense 2 (without accompaniment or companions):

unaccompanied

WordNet sense 3 (not seeking or given to association; being or living without companions):

unsocial

WordNet sense 4 (exclusive of anyone or anything else):

only

WordNet sense 5 (excluding much or all; especially all but a particular group or minority):

exclusive

WordNet sense 6 (radically distinctive and without equal):

unequaled, unequalled, unique, unparalleled

WordNet sense 7 (such that comparison is impossible; unsuitable for comparison or lacking features that can be compared):

incomparable, uncomparable

WordNet sense 8 (without anybody else):

solo

WordNet sense 9 (without any others being included or involved):

entirely, exclusively, solely