The Collaborative International Dictionary of English v.0.48:

Moodiness \Mood"i*ness\, n.
   The quality or state of being moody; specifically, liability
   to strange or violent moods.
   [1913 Webster]

WordNet (r) 3.0 (2006):

moodiness
    n 1: a sullen gloomy feeling
    2: having temperamental and changeable moods

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "moodiness":
   arbitrariness, bouderie, caprice, capriciousness, crankiness,
   crotchetiness, dejection, desultoriness, deviability, dumpishness,
   eccentricity, erraticism, fancifulness, fantasticality, fickleness,
   flightiness, freakishness, glumness, grimness, grumness,
   humorsomeness, impulsiveness, inconsistency, inconstancy,
   instability, irregularity, melancholy, mercuriality, moodishness,
   mopishness, moroseness, motivelessness, petulance, quirkiness,
   restlessness, shiftiness, sulkiness, sullenness, surliness,
   temperamentalness, uncertainty, undependability, unfixedness,
   unpredictability, unreliability, unsettledness, unstableness,
   unsteadfastness, unsteadiness, variability, variation, variety,
   wantonness, waywardness, whimsicality, whimsicalness, whimsy