The Collaborative International Dictionary of English v.0.48:
Auxiliary \Aux*il"ia*ry\, n.; pl. Auxiliaries.
1. A helper; an assistant; a confederate in some action or
2. (Mil.) pl. Foreign troops in the service of a nation at
war; (rarely in sing.), a member of the allied or
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; [^e]tre 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 formul[ae]. --Math. Dict.