Source : Webster's Revised Unabridged Dictionary (1913)

Welkin \Wel"kin\, n. [OE. welken, welkene, welkne, wolcne,
   weolcne, AS. wolcen, pl. wolcnu, a cloud; akin to D. wolk,
   OFries. wolken, OS. wolkan, G. wolke, OHG. wolchan, and
   probably to G. welk withered, OHG. welc moist, Russ. & OSlav.
   vlaga moisture, Lith. vilgyti to moisten.]
   The visible regions of the air; the vault of heaven; the sky.

         On the welkne shoon the sterres lyght.   --Chaucer.

         The fair welkin foully overcast.         --Spenser.

         When storms the welkin rend.             --Wordsworth.

   Note: Used adjectively by Shakespeare in the phase, ``Your
         welkin eye,'' with uncertain meaning.

Source : WordNet®

welkin
     n : the apparent surface of the imaginary sphere on which
         celestial bodies appear to be projected [syn: {celestial
         sphere}, {sphere}, {empyrean}, {firmament}, {heavens}, {vault
         of heaven}]