The Collaborative International Dictionary of English v.0.48:

malaria \ma*la"ri*a\, n. [It., contr. fr. malaaria bad air. See
   Malice, and Air.]
   1. Air infected with some noxious substance capable of
      engendering disease; esp., an unhealthy exhalation from
      certain soils, as marshy or wet lands, producing fevers;
      miasma. [Archaic]
      [1913 Webster]

   Note: The morbific agent in malaria is supposed by some to be
         a vegetable microbe or its spores, and by others to be
         a very minute animal blood parasite (an infusorian).
         [1913 Webster]

   2. (Med.) A human disease caused by infection of red blood
      cells by a protozoan of the genus Plasmodium, giving
      rise to fever and chills and many other symptoms,
      characterized by their tendency to recur at definite and
      usually uniform intervals. The protozoal infection is
      usually transmitted from another infected individual by
      the bite of an Anopheles mosquito.
      [1913 Webster +PJC] Malarian
      Malarial

WordNet (r) 3.0 (2006):

malaria
    n 1: an infective disease caused by sporozoan parasites that are
         transmitted through the bite of an infected Anopheles
         mosquito; marked by paroxysms of chills and fever