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.
(..) Varys? King Robert's spymaster? Yes, he's the one who convinced me to come find you. He was my travelling companion before Ser Jorah seized that role for himself. Jorah sent my secrets to Varys. For years the Spider oversaw (..)2015 TvShow: Game of Thrones Title: Hardhome Season: 5 Episode 8