AUXILIARY.

Synonyms:

accessory,ally,coadjutor,helper,promoter,
aid,assistant,confederate,mercenary,subordinate.

An auxiliary is a person or thing that helps in a subordinate[68] capacity. Allies unite as equals; auxiliaries are, at least technically, inferiors or subordinates. Yet the auxiliary is more than a mere assistant. The word is oftenest found in the plural, and in the military sense; auxiliaries are troops of one nation uniting with the armies, and acting under the orders, of another. Mercenaries serve only for pay; auxiliaries often for reasons of state, policy, or patriotism as well. Compare [ACCESSORY]; [APPENDAGE].

Antonyms:

antagonist,hinderer,opponent,opposer.

Prepositions:

The auxiliaries of the Romans; an auxiliary in a good cause; an auxiliary to learning.