Companion【n.】

1. a person or animal that you spend a lot of time with or that you travel with同伴，伴侣

She was my constant companion during those difficult times.

在那段困难时期，她一直是我忠实的伴侣。

2. one of a pair of things that go together or are used together成对物品之一

The companion volume will be published next month.

配套的卷册将于下月出版。

3. a person who is paid to live with and help somebody, especially an old or sick person受雇陪伴老人或病人的人

She works as a companion to an elderly lady.

她受雇陪伴一位老太太。

4. a book that gives you information about a particular subject or tells you how to do something指南，手册

The Oxford Companion to English Literature is a useful reference book.

《牛津英国文学指南》是一本有用的参考书。