The Collaborative International Dictionary of English v.0.48:

Kefir \Kef"ir\ (k[e^]f"[~e]r), n.
   1. An effervescent liquor like kumiss, made from fermented
      milk, used as a food and as a medicine in the northern
      Caucasus. -- Ke*fir"ic (k[e^]*f[i^]r"[i^]k), a.
      [Webster 1913 Suppl.]

   2. A sour fermented milk drink, used in various regions of
      Asia, made by addition of Streptococcus or
      Lactobacillus cultures to cow's or goat's milk; it is
      considered by some as a form of yoghurt.
      [PJC]