Source : Webster's Revised Unabridged Dictionary (1913)

Maxilla \Max*il"la\, n.; pl. {Maxill[ae]}. [L., dim. of mala
   jaw, jawbone.]
   1. (Anat.)
      (a) The bone of either the upper or the under jaw.
      (b) The bone, or principal bone, of the upper jaw, the
          bone of the lower jaw being the mandible. [Now
          commonly used in this restricted sense.]

   2. (Zo["o]l.) One of the lower or outer jaws of arthropods.

   Note: There are usually two pairs in Crustacea and one pair
         in insects. In certain insects they are not used as
         jaws, but may form suctorial organs. See Illust. under
         {Lepidoptera}, and {Diptera}.

Source : WordNet®

maxilla
     n : the upper jawbone in vertebrates; it is fused to the cranium
         [syn: {upper jaw}, {upper jawbone}]
     [also: {maxillae} (pl)]

maxillae
     See {maxilla}