The Collaborative International Dictionary of English v.0.48:

Pneumonia \Pneu*mo"ni*a\ (n[-u]*m[=o]"n[i^]*[.a]), n. [NL., fr.
   Gr. pneymoni`a, fr. pney`mwn, pl. pney`mones the lungs, also,
   pley`mwn, which is perh. the original form. Cf. Pneumatio,
   Pulmonary.] (Med.)
   Inflammation of the lungs.
   [1913 Webster]

   Note:

   Catarrhal pneumonia, or Broncho-pneumonia, is
      inflammation of the lung tissue, associated with catarrh
      and with marked evidences of inflammation of bronchial
      membranes, often chronic; -- also called lobular
      pneumonia, from its affecting single lobules at a time.


   Croupous pneumonia, or ordinary pneumonia, is an acute
      affection characterized by sudden onset with a chill, high
      fever, rapid course, and sudden decline; -- also called
      lobar pneumonia, from its affecting a whole lobe of the
      lung at once. See under Croupous.

   Fibroid pneumonia is an inflammation of the interstitial
      connective tissue lying between the lobules of the lungs,
      and is very slow in its course, producing shrinking and
      atrophy of the lungs.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pneumonia
    n 1: respiratory disease characterized by inflammation of the
         lung parenchyma (excluding the bronchi) with congestion
         caused by viruses or bacteria or irritants

Moby Thesaurus II by Grady Ward, 1.0:

186 Moby Thesaurus words for "pneumonia":
   African lethargy, Asiatic cholera, Asiatic flu, Chagres fever,
   German measles, Haverhill fever, Hong Kong flu,
   acute articular rheumatism, acute bronchitis, adenoiditis, ague,
   alkali disease, aluminosis, amebiasis, amebic dysentery,
   amygdalitis, anthracosilicosis, anthracosis, anthrax, asbestosis,
   asthma, atypical pneumonia, bacillary dysentery, bastard measles,
   bituminosis, black death, black fever, black lung,
   blackwater fever, breakbone fever, bronchial pneumonia,
   bronchiectasis, bronchiolitis, bronchitis, bronchopneumonia,
   brucellosis, bubonic plague, cachectic fever, catarrh,
   cerebral rheumatism, chalicosis, chicken pox, cholera,
   chronic bronchitis, cold, collapsed lung, common cold, coniosis,
   coryza, cowpox, croup, croupous pneumonia, dandy fever,
   deer fly fever, dengue, dengue fever, diphtheria, double pneumonia,
   dry pleurisy, dumdum fever, dysentery, elephantiasis, emphysema,
   empyema, encephalitis lethargica, enteric fever,
   epidemic pleurodynia, erysipelas, famine fever,
   fibrinous pneumonia, five-day fever, flu, frambesia,
   glandular fever, grippe, hansenosis, hay fever, hepatitis, herpes,
   herpes simplex, herpes zoster, histoplasmosis, hookworm,
   hydrophobia, infantile paralysis, infectious mononucleosis,
   inflammatory rheumatism, influenza, jail fever, jungle rot,
   kala azar, kissing disease, la grippe, laryngitis, lepra, leprosy,
   leptospirosis, lipoid pneumonia, loa loa, loaiasis,
   lobar pneumonia, lockjaw, lung cancer, lung fever, madness,
   malaria, malarial fever, marsh fever, measles, meningitis,
   milzbrand, mumps, ornithosis, osteomyelitis, paratyphoid fever,
   parotitis, parrot fever, pertussis, pharyngitis, pleurisy,
   pleuritis, pneumococcal pneumonia, pneumoconiosis, pneumonic fever,
   pneumothorax, polio, poliomyelitis, polyarthritis rheumatism,
   ponos, psittacosis, quinsy, rabbit fever, rabies, rat-bite fever,
   relapsing fever, rheum, rheumatic fever, rickettsialpox, ringworm,
   rubella, rubeola, scarlatina, scarlet fever, schistosomiasis,
   septic sore throat, shingles, siderosis, silicosis,
   sleeping sickness, sleepy sickness, smallpox, snail fever,
   sore throat, splenic fever, spotted fever, strep throat,
   swamp fever, swine flu, tetanus, the sniffles, the snuffles,
   thrush, tinea, tonsilitis, trench fever, trench mouth,
   tuberculosis, tularemia, typhoid, typhoid fever, typhus,
   typhus fever, undulant fever, vaccinia, varicella, variola,
   venereal disease, viral dysentery, virus pneumonia, wet pleurisy,
   whooping cough, yaws, yellow fever, yellow jack, zona, zoster