Synonyms for Auxiliary:

adj.

accompanying (adjective)
adjoining, attached, ornamental, affixed, secondary, in addition to, Adorning, companion, extra, along with, additional, supplemental, besides.
additional (adjective)
supplemental.
all (adjective)
supplemental, supplementary, subsidiary.
assisting (adjective)
Aiding, helping, supporting, Assisting, serving, Cooperating, Sustaining, helpful.
relational (adjective)
concomitant, blood, affiliated, germane, akin, analogous, adjunct, relevant, associated, connected, correlative, consanguine, ancillary, dependent, coincident, attendant, pertinent, kindred, supplemental, related.
supplementary (adjective)
backup, subsidiary, reserve, secondary, ancillary, spare, adjuvant, extra, supporting, appurtenant, subordinate, supplementary, contributory, accessory.
supporting (adjective)
supporting.

n.

administrative assistant, advance person, ally. emeritus, blue-collar, designate, collateral, contributory, acting, casual, creative, budding. automatic, broken, clean, automatically, standby, emergency, clockwork, increase, reserve, cordless, analog, clever, built. copula, the first person, coadjutor, the future, the active, aspect, the conditional, DO, conjugation, Coadjutant, auxiliary verb. accompaniment (noun)
appendix, ornament, garnish, secondary, companion, consort, attachment, adornment, extension, appendage, addendum, addition, brother, fixture, accompaniment, appurtenance.
agent (noun)
factor, instrument, impresario, broker, actor, intermediary, liaison, middleman, agency, mediator, vehicle, ombudsman, operative, go-between, executor.
assistant (noun)
chaperone, acolyte, attendant, servant, helper, agent, second, accomplice, underling, abettor, extra, menial, associate, hireling, flunky, attorney, functionary, deputy, aide-de-camp, aide, employee, assistant, Aider, backer, junior, accessory, laborer, patsy, ancillary, proxy, adjunct, helpmate, lieutenant, follower, stooge, minion, partner, benefactor, henchman, subordinate.
auxiliary (noun)
aide, supplementary, adjunct, supportive, subsidiary, accessory, supplemental, appurtenant, adjuvant, ancillary, secondary.
deputy (noun)
double, dummy, nominee, envoy, substitute, token, mouthpiece, understudy, delegate, ghost, surrogate, appointee, representative, backup, assignee, spokeswoman, arm, figurehead, stand in, emissary, alternate, spokesman.
helper (noun)
assistant, ally, accomplice, companion, partner, associate.
inferior (noun)
junior, menial.
person (noun)
aide.
servant (noun)
volunteer, aid, worker, hand, serf, subject, helping hand, chattel, pawn, vassal, help, peon.
substitute (noun)
substitute.
supplementary (noun)
reserve, spare.

Other synonyms:

contributory, creative, cordless, built, acting, designate, emeritus, Coadjutant, blue-collar, standby, the conditional, auxiliary verb, the active, copula, conjugation. automatically, the first person, coadjutor, analog, broken. casual, collateral. automatic, clever, aspect. reserve. DO. Other relevant words:
built, reserve, creative, budding, acting, ally, Coadjutant, clockwork, casual, auxiliary verb, adjuvant, coadjutor, spare, automatically, contributory, increase, subsidiary, broken, emergency, designate, aspect, automatic, clever, blue-collar, appurtenant, copula, standby, DO, collateral, cordless, supplementary, emeritus, conjugation, analog, clean, supportive.

Usage examples for auxiliary

  1. 6. Auxiliary derived from the idea of power, dependent upon circumstances internal to the agent- can. – The English Language by Robert Gordon Latham
  2. The answer should have the same auxiliary as the question. – Slips of Speech by John H. Bechtel