Source : Webster's Revised Unabridged Dictionary (1913)

Alter \Al"ter\, v. t. [imp. & p. p. {Altered}; p. pr. & vb. n.
   {Altering}.] [F. alt['e]rer, LL. alterare, fr. L. alter
   other, alius other. Cf. {Else}, {Other}.]
   1. To make otherwise; to change in some respect, either
      partially or wholly; to vary; to modify. ``To alter the
      king's course.'' ``To alter the condition of a man.'' ``No
      power in Venice can alter a decree.'' --Shak.

            It gilds all objects, but it alters none. --Pope.

            My covenant will I not break, nor alter the thing
            that is gone out of my lips.          --Ps. lxxxix.
                                                  34.

   2. To agitate; to affect mentally. [Obs.] --Milton.

   3. To geld. [Colloq.]

   Syn: {Change}, {Alter}.

   Usage: Change is generic and the stronger term. It may
          express a loss of identity, or the substitution of one
          thing in place of another; alter commonly expresses a
          partial change, or a change in form or details without
          destroying identity.

Source : WordNet®

altering
     n : the sterilization of an animal; "they took him to the vet
         for neutering" [syn: {neutering}, {fixing}]