A person habitually or temporarily in the company of another specified person; a companion, an associate, a comrade; (also) a companion in a…

Apparently a boon companion.

a friend who agrees absolutely with one's tastes and opinions, or for whose welfare one cares as much as for one's own.

dear heart: a boon companion; a fine or brave fellow (in Dryden, as if one of a set or group). Obsolete. rare.

colloquial. A friend, a drinking companion. Obsolete. rare.

fellow well met: a person who is companionable, sociable, or convivial. Similarly to be fellow-well-met: to be on friendly or familiar terms with a…

A sailor. Also: a brave person; a good fellow. Now rare.

Originally U.S. slang. A companion or close associate; esp. a loyal assistant of a more important or powerful person; (also) a partner in crime, an…

A companion, an assistant, an accomplice; = sidekick, n. 3.