Companion (noun)

1. A person who frequently spends time with another.
2. A thing that goes well with another.
3. A companion animal, such as a pet.

Origin:

Derived from the old french word 'compagnon' meaning 'a comrade'.

Examples:

1. He was her constant companion on her travels.
2. The cake is the perfect companion to a cup of coffee.
3. Her loyal dog was her faithful companion throughout her life.