The Collaborative International Dictionary of English v.0.48:

Encephalitis \En*ceph`a*li"tis\, n. [NL., from Gr. 'egke`falos
   the brain + -itis.] (Med.)
   Inflammation of the brain. -- En`ceph*a*lit"ic, a.
   [1913 Webster]

WordNet (r) 3.0 (2006):

encephalitis
    n 1: inflammation of the brain usually caused by a virus;
         symptoms include headache and neck pain and drowsiness and
         nausea and fever (`phrenitis' is no longer in scientific
         use) [syn: encephalitis, cephalitis, phrenitis]

Moby Thesaurus II by Grady Ward, 1.0:

131 Moby Thesaurus words for "encephalitis":
   adenoiditis, adrenitis, appendicitis, arteritis,
   arthritis deformans, arthritis fungosa, arthritis pauperum,
   atrophic arthritis, atrophic inflammation, blennorrhagic arthritis,
   brain fever, bronchitis, bunion, bursitis, capillaritis, carditis,
   catarrh, catarrhal inflammation, cerebellitis, cerebral meningitis,
   cerebritis, cerebrospinal meningitis, chronic infectious arthritis,
   chronic inflammation, cirrhotic inflammation, climactic arthritis,
   clitoritis, colitis, collagen disease, conjunctivitis, cystitis,
   degenerative arthritis, diffuse inflammation, endocarditis,
   enteritis, equine encephalomyelitis, exudative inflammation,
   fibroid inflammation, focal inflammation, gastritis, gingivitis,
   glossitis, gonococcal arthritis, gonorrheal arthritis,
   gonorrheal rheumatism, gout, gouty arthritis, hemophilic arthritis,
   hepatitis, hyperplastic inflammation, hypertrophic arthritis,
   hypertrophic inflammation, infectional arthritis,
   infectious hepatitis, inflammation, irritable bowel syndrome,
   laryngitis, lumbago, lumbar rheumatism, mastoiditis, meningitis,
   menopausal arthritis, metastatic inflammation, metritis, milk leg,
   mucous colitis, mumps meningitis, myelitis, necrotic inflammation,
   nephritis, neuritis, obliterative inflammation, ophthalitis,
   ophthalmia, orchitis, osseous rheumatism, osteitis, osteoarthritis,
   osteomyelitis, otitis, ovaritis, paradental pyorrhea, penitis,
   pericarditis, periodontitis, peritonitis, pharyngitis, phlebitis,
   podagra, proliferative arthritis, prostatitis, pyonephritis,
   pyorrhea, pyorrhea alveolaris, reactive inflammation, rheumatism,
   rheumatiz, rheumatoid arthritis, rhinitis, sclerosing inflammation,
   seroplastic inflammation, serous inflammation, serum hepatitis,
   simple inflammation, sinusitis, spastic colon,
   specific inflammation, subacute rheumatism, suppurative arthritis,
   suppurative inflammation, syphilitic arthritis, tennis elbow,
   testitis, thrombophlebitis, tonsilitis, torticollis,
   toxic inflammation, traumatic inflammation, tuberculous arthritis,
   tuberculous rheumatism, ulcerative colitis, uratic arthritis,
   ureteritis, urethral arthritis, urethritis, uteritis, vaginitis,
   vertebral arthritis, visceral rheumatism, vulvitis, wryneck