Source : Webster's Revised Unabridged Dictionary (1913)

Ox \Ox\ ([o^]ks), n.; pl. {Oxen}. [AS. oxa; akin to D. os. G.
   ochs, ochse, OHG. ohso, Icel. oxi, Sw. & Dan. oxe, Goth.
   a['u]hsa, Skr. ukshan ox, bull; cf. Skr. uksh to sprinkle.
   [root]214. Cf. {Humid}, {Aurochs}.] (Zo["o]l.)
   The male of bovine quadrupeds, especially the domestic animal
   when castrated and grown to its full size, or nearly so. The
   word is also applied, as a general name, to any species of
   bovine animals, male and female.

         All sheep and oxen, yea, and the beasts of the field.
                                                  --Ps. viii. 7.

   Note: The castrated male is called a steer until it attains
         its full growth, and then, an ox; but if castrated
         somewhat late in life, it is called a stag. The male,
         not castrated, is called a bull. These distinctions are
         well established in regard to domestic animals of this
         genus. When wild animals of this kind are spoken of, ox
         is often applied both to the male and the female. The
         name ox is never applied to the individual cow, or
         female, of the domestic kind. Oxen may comprehend both
         the male and the female.

   {Grunting ox} (Zo["o]l.), the yak.

   {Indian ox} (Zo["o]l.), the zebu.

   {Javan ox} (Zo["o]l.), the banteng.

   {Musk ox}. (Zo["o]l.) See under {Musk}.

   {Ox bile}. See {Ox gall}, below.

   {Ox gall}, the fresh gall of the domestic ox; -- used in the
      arts and in medicine.

   {Ox pith}, ox marrow. [Obs.] --Marston.

   {Ox ray} (Zo["o]l.), a very large ray ({Dicerobatis
      Giorn[ae]}) of Southern Europe. It has a hornlike organ
      projecting forward from each pectoral fin. It sometimes
      becomes twenty feet long and twenty-eight feet broad, and
      weighs over a ton. Called also {sea devil}.

   {To have the black ox tread on one's foot}, to be
      unfortunate; to know what sorrow is (because black oxen
      were sacrificed to Pluto). --Leigh Hunt.

Source : WordNet®

oxen
     n : domesticated bovine animals as a group regardless of sex or
         age; "so many head of cattle"; "wait till the cows come
         home"; "seven thin and ill-favored kine"- Bible; "a team
         of oxen" [syn: {cattle}, {cows}, {kine}, {Bos taurus}]

ox
     n 1: an adult castrated bull of the genus Bos; especially Bos
          taurus
     2: any of various wild bovines especially of the genera Bos or
        closely related Bibos [syn: {wild ox}]
     [also: {oxen} (pl)]

oxen
     See {ox}