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.
(..) - Phenomenal film. Science fiction, but overlooked in the genre. It's about a botanist who's marooned on a space freighter. His only companions are three little robots that look like TV sets. He names them Huey, Dewey and Louie. - They play poker with him. - They sound adorable. They are. (..)2003 TvShow: Six Feet Under Title: Making Love Work Season: 3 Episode 6