\Aux*il"ia*ry\ (?; 106), a. [L. auxiliarius, fr.
auxilium help, aid, fr. augere to increase.]
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.

\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; [^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.