Source : Webster's Revised Unabridged Dictionary (1913)

Stoma \Sto"ma\, n.; pl. {Stomata}. [NL., fr. Gr. ?, ?, a mouth.]
   1. (Anat.) One of the minute apertures between the cells in
      many serous membranes.

   2. (Bot.)
      (a) The minute breathing pores of leaves or other organs
          opening into the intercellular spaces, and usually
          bordered by two contractile cells.
      (b) The line of dehiscence of the sporangium of a fern. It
          is usually marked by two transversely elongated cells.
          See Illust. of {Sporangium}.

   3. (Zo["o]l.) A stigma. See {Stigma}, n., 6
      (a) &
      (b) .

Source : WordNet®

stoma
     n 1: a minute epidermal pore in a leaf or stem through which
          gases and water vapor can pass [syn: {stomate}, {pore}]
     2: a mouth or mouthlike opening (especially one created by
        surgery on the surface of the body to create an opening to
        an internal organ)
     [also: {stomata} (pl)]