a person or an animal that travels with you or spends a lot of time with you

a person who shares your experiences, especially when these are particularly pleasant or unpleasant

She was a charming dinner companion.

His younger brother is not much of a companion for him.

They're drinking companions .

We became companions in misfortune.

He was an entertaining dinner companion.

a person, usually a woman, employed to live with and help somebody, especially somebody old or ill

She lived in the house as a companion to our grandmother.

one of a pair of things that go together or can be used together

A companion volume is soon to be published.

used in book titles to describe a book giving useful facts and information on a particular subject

LEARNit Dictionary