Source : Webster's Revised Unabridged Dictionary (1913)

Hors d'oeuvre \Hors` d'[oe]uvre"\; pl. {Hors d'[oe]uveres}. [F.,
   lit., outside of work.]
   1. Something unusual or extraordinary. [R.]

   2. A dish served as a relish, usually at the beginning of a
      meal.

Source : WordNet®

hors d'oeuvre
     n : a dish served as an appetizer before the main meal