Source : Webster's Revised Unabridged Dictionary (1913)

Yak \Yak\ (y[a^]k), n. [Thibetan gyag.] (Zo["o]l.)
   A bovine mammal ({Po["e]phagus grunnies}) native of the high
   plains of Central Asia. Its neck, the outer side of its legs,
   and its flanks, are covered with long, flowing, fine hair.
   Its tail is long and bushy, often white, and is valued as an
   ornament and for other purposes in India and China. There are
   several domesticated varieties, some of which lack the mane
   and the long hair on the flanks. Called also {chauri gua},
   {grunting cow}, {grunting ox}, {sarlac}, {sarlik}, and
   {sarluc}.

   {Yak lace}, a coarse pillow lace made from the silky hair of
      the yak.

Source : WordNet®

yak
     n 1: noisy talk [syn: {yack}, {yakety-yak}, {chatter}, {cackle}]
     2: large long-haired wild ox of Tibet often domesticated [syn:
        {Bos grunniens}]
     [also: {yakking}, {yakked}]