One who keeps company with another; one with whom a person frequently associates, and converses. It differs from friend, says Johnson, as acquaintance from confidence. The word does not necessarily imply friendship; but a companion is often or generally a friend. A companion of fools shall be destroyed. Proverbs 13:20.

One who accompanies another; as two persons meeting casually and traveling together are called companions. So soldiers are called companions in arms.

A partner; an associate. Epaphroditus, my brother, and companion in labor, and fellow soldier. Philippians 2:25.

A fellow; a mate.

A sort of wooden porch placed over the entrance or stair case of the cabin in merchant ships. Hence the ladder by which officers ascend to and descend from the quarter deck is called the companion ladder.