Synonyms for Companion:

adj.

accompanying (adjective)
affixed, additional, extra, attached, besides, adjoining, along with, Adorning, auxiliary, in addition to, secondary, ornamental, supplemental.

n.

firm friends, confidante, girlfriend. connection, association, chemistry, guide, protector, chaperon, nurse, escort, rapport, link, partnership, reconciliation, relations, practical nurse, governess, matron, tie, safeguard, relationship. anthology, annual, bestseller, blook, biography, near, atlas, authority, bible, autobiography, almanac. concomitant, section, segment, unit, detail, portion, bit, piece, substructure, subdivision, part, accompanied. double, camp follower, commuter, same, match, coach party, business traveler, counterpart, explorer, backpacker, twin, duplicate, bird of passage, caravan. attend, go hand in hand with. accompaniment (noun)
adjunct, appendage, addition, extra, garnish, auxiliary, brother, extension, attachment, ornament, second, appurtenance, fixture, consort, accessory, lieutenant, addendum, secondary, appendix, accompaniment, adornment.
assistant (noun)
lieutenant.
companion (noun)
fellow, associate, fellow traveller, fellow traveler, company, accompany, comrade, keep company, Familiar.
friend (noun)
classmate, buddy, playmate, friend, comrade, cousin, confidant, intimate, Familiar, partner, chum, ally, sister, company, schoolmate, pal, amigo, fellow, crony, mate, teammate, co-worker, acquaintance, roommate, colleague.
girlfriend (noun)
girlfriend.
helper, friend (noun)
chaperon, match, buddy, colleague, associate, cousin, consort, nurse, mate, co-worker, concomitant, crony, ally, pal, double, comrade, counterpart, accompaniment, protector, guide, partner, escort, playmate, safeguard.
person (noun)
fellow traveller, Familiar, associate, fellow, comrade, fellow traveler.

v.

stative (verb)
keep company, accompany, company.

Other synonyms:

confidante, bird of passage, girlfriend, explorer, business traveler, backpacker, caravan, coach party, firm friends. twin, camp follower, connection, commuter. duplicate. counterpart, match. attend. escort
chaperon.
guide
escort.
Other relevant words:
commuter, keep company, chaperon, confidante, attend, explorer, duplicate, matron, match, concomitant, double, fellow traveler, associate, nurse, fellow traveller, counterpart, escort, accompany, twin, guide, protector, girlfriend, safeguard, go hand in hand with.

Usage examples for companion

  1. " And aunt," replied Will quietly; and there was so much meaning in his tone that his companion did not ask the question upon his lips about father and mother. – Menhardoc by George Manville Fenn
  2. " That's nothing," retorted Frettlby, looking at his companion sharply. – The Mystery of a Hansom Cab by Fergus Hume
  3. " Yore right," replied his companion – Hopalong Cassidy's Rustler Round-Up Bar-20 by Clarence Edward Mulford