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

Moby Thesaurus II by Grady Ward, 1.0:

153 Moby Thesaurus words for "malaria":
   African lethargy, Asiatic cholera, Chagres fever, German measles,
   Haverhill fever, acute articular rheumatism, afterdamp, ague,
   alkali disease, amebiasis, amebic dysentery, anthrax,
   bacillary dysentery, bastard measles, black death, black fever,
   blackdamp, blackwater fever, breakbone fever, breath, brucellosis,
   bubonic plague, cachectic fever, cerebral rheumatism, chicken pox,
   chokedamp, cholera, cloud, coal gas, cowpox, damp, dandy fever,
   deer fly fever, dengue, dengue fever, diphtheria, dumdum fever,
   dysentery, effluvium, elephantiasis, encephalitis lethargica,
   enteric fever, erysipelas, exhalation, exhaust, exhaust gas,
   famine fever, fetid air, firedamp, five-day fever, flatus, flu,
   fluid, frambesia, fume, glandular fever, grippe, hansenosis,
   hepatitis, herpes, herpes simplex, herpes zoster, histoplasmosis,
   hookworm, hydrophobia, infantile paralysis,
   infectious mononucleosis, inflammatory rheumatism, influenza,
   jail fever, jungle rot, kala azar, kissing disease, lepra, leprosy,
   leptospirosis, loa loa, loaiasis, lockjaw, madness, malarial fever,
   marsh fever, measles, meningitis, mephitis, miasma, milzbrand,
   mumps, ornithosis, osteomyelitis, paratyphoid fever, parotitis,
   parrot fever, pertussis, pneumonia, polio, poliomyelitis,
   polyarthritis rheumatism, ponos, psittacosis, puff of smoke,
   rabbit fever, rabies, rat-bite fever, reek, relapsing fever,
   rheumatic fever, rickettsialpox, ringworm, rubella, rubeola,
   scarlatina, scarlet fever, schistosomiasis, septic sore throat,
   shingles, sleeping sickness, sleepy sickness, smallpox, smoke,
   smudge, snail fever, splenic fever, spotted fever, steam,
   strep throat, swamp fever, tetanus, thrush, tinea, trench fever,
   trench mouth, tuberculosis, tularemia, typhoid, typhoid fever,
   typhus, typhus fever, undulant fever, vaccinia, vapor, varicella,
   variola, venereal disease, viral dysentery, volatile, water vapor,
   whooping cough, yaws, yellow fever, yellow jack, zona, zoster