n. 25B6; noun
Harry and his companion : ASSOCIATE, partner, escort, compatriot, confederate; friend, intimate, confidant(e), comrade; informal pal, chum, crony, sidekick; Brit. informal mate, oppo, china, mucker; N. Amer. informal buddy, amigo, compadre; Austral./NZ informal offsider.
a lady's companion : ATTENDANT, aide, helper, assistant, valet, equerry, lady in waiting; chaperone; carer, minder.
the tape is a companion to the book : COMPLEMENT, counterpart, twin, match; accompaniment, supplement, addition, adjunct, accessory.
The Gardener's Companion : HANDBOOK, manual, guide, reference book, ABC, primer, vade mecum; informal bible.