Solitary; having no companion. / Isolated or lonely; lacking companionship. / Sole; being the only one of a type. / Situated by itself or by oneself, with no neighbours.

Unhappy because of feeling isolated from contact with other people. / (of a place or time) Unfrequented by people; desolate. / (of a person) Without companions; solitary.

(idiomatic) To go alone.

(now rare) The state of being alone; loneliness, solitariness.

Of a newspaper column: in which people attempt to find friends of the opposite sex.

plural of lonely-heart

(informal) A person with no friends of the opposite sex who is looking for a spouse or companion

A hero of westerns who wore a mask. / A solitary, sometimes mysterious or heroic, person.

A wolf that is not part of a pack. / (figuratively) A person who avoids the company of others; a loner; an independent or solitary person.

(chemistry) A pair of electrons in the valence shell of an atom that does not participate in bonding.