The Collaborative International Dictionary of English v.0.48:

Fibrillation \Fi`bril*la"tion\, n.
   The state of being reduced to fibers. --Carpenter.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fibrillation
    n 1: muscular twitching involving individual muscle fibers
         acting without coordination
    2: act or process of forming fibrils

Moby Thesaurus II by Grady Ward, 1.0:

105 Moby Thesaurus words for "fibrillation":
   abscess, ague, anemia, ankylosis, anoxia, apnea, arrhythmia,
   asphyxiation, asthma, ataxia, atrophy, backache, bleeding,
   blennorhea, brokenness, cachexia, cachexy, capriciousness, chill,
   chills, choppiness, colic, constipation, convulsion, coughing,
   cyanosis, desultoriness, diarrhea, disconnectedness, discontinuity,
   dizziness, dropsy, dysentery, dyspepsia, dyspnea, eccentricity,
   edema, emaciation, erraticness, fainting, fatigue, fever,
   fitfulness, fits and starts, fluctuation, flux, growth, hemorrhage,
   high blood pressure, hydrops, hypertension, hypotension, icterus,
   inconstancy, indigestion, inflammation, insomnia, intermittence,
   irregularity, itching, jaundice, jerkiness, labored breathing,
   low blood pressure, lumbago, marasmus, nasal discharge, nausea,
   necrosis, nonuniformity, pain, paralysis, patchiness, pruritus,
   rash, rheum, roughness, sclerosis, seizure, shock, skin eruption,
   sneezing, sore, spasm, spasticity, sporadicity, sporadicness,
   spottiness, stagger, tabes, tachycardia, tumor, uncertainty,
   unevenness, unmethodicalness, unpredictability, unsteadiness,
   unsystematicness, upset stomach, variability, vertigo, vomiting,
   wasting, whimsicality, wobble