Auxiliary

Part of speech: noun (n.)

1. A helper; an assistant; a confederate in some action or enterprise.

2. Foreign troops in the service of a nation at war; (rarely in sing.), a member of the allied or subsidiary force.

3. A verb which helps to form the voices, modes, and tenses of other verbs; -- called, also, an auxiliary verb; as, have, be, may, can, do, must, shall, and will, in English; être and avoir, in French; avere and essere, in Italian; estar and haber, in Spanish.

4. A quantity introduced for the purpose of simplifying or facilitating some operation, as in equations or trigonometrical formulæ. Math. Dict.

Part of speech: adjective (a.)

Conferring aid or help; helping; aiding; assisting; subsidiary; as auxiliary troops. Auxiliary scales (Mus.), the scales of relative or attendant keys. See under Attendant, a. -- Auxiliary verbs (Gram.). See Auxiliary, n., 3.