Source : Webster's Revised Unabridged Dictionary (1913)

Yawn \Yawn\ (y[add]n), v. i. [imp. & p. p. {Yawned}; p. pr. &
   vb. n. {Yawning}.] [OE. yanien, [yogh]anien, ganien, gonien,
   AS. g[=a]nian; akin to ginian to yawn, g[=i]nan to yawn, open
   wide, G. g["a]hnen to yawn, OHG. gin[=e]n, gein[=o]n, Icel.
   g[=i]na to yawn, gin the mouth, OSlav. zijati to yawn, L.
   hiare to gape, yawn; and perhaps to E. begin, cf. Gr. cheia`
   a hole. [root]47b. Cf. Begin, Gin to begin, {Hiatus}.]
   1. To open the mouth involuntarily through drowsiness,
      dullness, or fatigue; to gape; to oscitate. ``The lazy,
      yawning drone.'' --Shak.

            And while above he spends his breath, The yawning
            audience nod beneath.                 --Trumbull.

   2. To open wide; to gape, as if to allow the entrance or exit
      of anything.

            't is now the very witching time of night, When
            churchyards yawn.                     --Shak.

   3. To open the mouth, or to gape, through surprise or
      bewilderment. --Shak.

   4. To be eager; to desire to swallow anything; to express
      desire by yawning; as, to yawn for fat livings. ``One
      long, yawning gaze.'' --Landor.

Yawn \Yawn\, n.
   1. An involuntary act, excited by drowsiness, etc.,
      consisting of a deep and long inspiration following
      several successive attempts at inspiration, the mouth,
      fauces, etc., being wide open.

            One person yawning in company will produce a
            spontaneous yawn in all present.      --N. Chipman.

   2. The act of opening wide, or of gaping. --Addison.

   3. A chasm, mouth, or passageway. [R.]

            Now gape the graves, and trough their yawns let
            loose Imprisoned spirits.             --Marston.

Source : WordNet®

yawn
     n : an involuntary intake of breath through a wide open mouth;
         usually triggered by fatigue or boredom; "he could not
         suppress a yawn"; "the yawning in the audience told him
         it was time to stop"; "he apologized for his ostinancy"
         [syn: {yawning}, {oscitance}, {oscitancy}]
     v 1: utter a yawn, as from lack of oxygen or when one is tired;
          "The child yawned during the long performance"
     2: be wide open; "the deep gaping canyon" [syn: {gape}, {yaw}]