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.

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.

(idiomatic) To go alone.

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

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

plural of lonely-heart

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

Yearning for affection and companionship.

The quality of being lonely-hearted.

A highly successful person in a particular field will inevitably suffer from a feeling of isolation.