Aux·il·ia·ry, n.; pl. Auxiliaries
1. A helper; an assistant; a confederate in some action or enterprise.
2. Mil. pl. Foreign troops in the service of a nation at war; (rarely in sing.), a member of the allied or subsidiary force.
3. Gram. 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. Math. A quantity introduced for the purpose of simplifying or facilitating some operation, as in equations or trigonometrical formulæ.