Source : Webster's Revised Unabridged Dictionary (1913)

Inconstancy \In*con"stan*cy\, n. [L. inconstantia.]
   The quality or state of being inconstant; want of constancy;
   mutability; fickleness; variableness.

         For unto knight there was no greater shame, Than
         lightness and inconstancie in love.      --Spenser.

Source : WordNet®

inconstancy
     n 1: unfaithfulness by virtue of being unreliable or treacherous
          [syn: {faithlessness}, {falseness}, {fickleness}]
     2: the quality of being changeable and variable [syn: {changefulness}]
        [ant: {constancy}]