The Collaborative International Dictionary of English v.0.48:

Kaffir \Kaf"fir\ (k[a^]f"f[~e]r), Kafir \Ka"fir\
   (k[aum]"f[~e]r), n. [Ar. k[=a]fir infidel, pagan, fr. kafara
   to be skeptical in religious matters; -- a name given to
   certain infidel races by the Mohammedans. Cf. Giaour.]
   1. (Ethnol.)
      (a) One of a race which, with the Hottentots and Bushmen,
          inhabit South Africa. They inhabit the country north
          of Cape Colony, the name being now specifically
          applied to the tribes living between Cape Colony and
          Natal, including the Ponda, Xosa, and Tembu; but the
          Zulus of Natal are true Kaffirs.
      (b) One of a race inhabiting Kafiristan in Central Asia.
          [Spelt also Caffre.]
          [1913 Webster]

   2. Any Black African; -- a disparaging and offensive term
      used by white South Africans. [South Africa]

   Syn: kaffir, caffer, caffre.
        [WordNet 1.5]

   Kaffir corn (Bot.), a Cape Colony name for Indian millet.
      [1913 Webster]

WordNet (r) 3.0 (2006):

kaffir
    n 1: important for human and animal food; growth habit and stem
         form similar to Indian corn but having sawtooth-edged
         leaves [syn: great millet, kaffir, kafir corn,
         kaffir corn, Sorghum bicolor]
    2: an offensive and insulting term for any Black African [syn:
       kaffir, kafir, caffer, caffre]