Source : Webster's Revised Unabridged Dictionary (1913)

Erratic \Er*rat"ic\, n.
   1. One who deviates from common and accepted opinions; one
      who is eccentric or preserve in his intellectual
      character.

Erratic \Er*rat"ic\, a. [L. erraticus, fr. errare to wander: cf.
   F. erratique. See {Err}.]
   1. Having no certain course; roving about without a fixed
      destination; wandering; moving; -- hence, applied to the
      planets as distinguished from the fixed stars.

            The earth and each erratic world.     --Blackmore.

   2. Deviating from a wise of the common course in opinion or
      conduct; eccentric; strange; queer; as, erratic conduct.

   3. Irregular; changeable. ``Erratic fever.'' --Harvey.

   {Erratic blocks}, {gravel, etc.} (Geol.), masses of stone
      which have been transported from their original resting
      places by the agency of water, ice, or other causes.

   {Erratic phenomena}, the phenomena which relate to
      transported materials on the earth's surface.

Source : WordNet®

erratic
     adj 1: having no fixed course; "an erratic comet"; "his life
            followed a wandering course"; "a planetary vagabond"
            [syn: {planetary}, {wandering}]
     2: liable to sudden unpredictable change; "erratic behavior";
        "fickle weather"; "mercurial twists of temperament"; "a
        quicksilver character, cool and willful at one moment,
        utterly fragile the next" [syn: {fickle}, {mercurial}, {quicksilver(a)}]
     3: likely to perform unpredictably; "erratic winds are the bane
        of a sailor"; "a temperamental motor; sometimes it would
        start and sometimes it wouldn't"; "that beautiful but
        temperamental instrument the flute"- Osbert Lancaster
        [syn: {temperamental}]