Source : Webster's Revised Unabridged Dictionary (1913)

Wether \Weth"er\, n. [OE. wether, AS. we[eth]er; akin to OS.
   wethar, withar, a ram, D. weder, G. widder, OHG. widar, Icel.
   ve[eth]r, Sw. v["a]dur, Dan. v[ae]dder, Goth. wi[thorn]rus a
   lamb, L. vitulus calf, Skr. vatsa, L. vetus old, Gr. 'e`tos
   year; -- originally meaning, a yearling. Cf. {Veal},
   {Veteran}.]
   A castrated ram.

Source : WordNet®

wether
     n : male sheep especially a castrated one