The old dog had been her 'constant companion' for over 12 years. [=had been with her most of the time for 12 years]
The book is a 'companion to' the television series with the same name.
The book is the 'companion' volume 'to' his previous book on jazz.
(..) I'm the insulte party, Lor Baelish. Ser Loras was promise to me. Instea he chose the company of boys. One's choice of companion is a curious thing. Most curious. Lysa Arryn, for instance. Thoroughly repellant woman. Forgive me. (..)2015 TvShow: Game of Thrones Title: Unbowed, Unbent, Unbroken Season: 5 Episode 6
(..) berries an roots. I can. You're not hungry? Of course I'm hungry. You're an awful travelling companion, o you know that? Possibly the least charming man I've ever met. I'm not your travelling companion. We are travelling together in (..)2015 TvShow: Game of Thrones Title: Unbowed, Unbent, Unbroken Season: 5 Episode 6