Source : Webster's Revised Unabridged Dictionary (1913)

Spay \Spay\, v. t. [imp. & p. p. {Spayed}; p. pr. & vb. n.
   {Spaying}.] [Cf. Armor. spac'hein, spaza to geld, W. dyspaddu
   to geld, L. spado a eunuch, Gr. ?.]
   To remove or extirpate the ovaries of, as a sow or a bitch;
   to castrate (a female animal).

Source : WordNet®

spaying
     n : neutering a female by removing the ovaries