adjective (a)

• likely to change frequently often without apparent or cogent reason; variable(adj.all)

  Example:
  Inconstant affections.
  An inconstant lover.
  Swear not by...the inconstant moon.
  

  Antonym:
  constant
  

  source: wordnet30
• Not constant; not stable or uniform; subject to change of character, appearance, opinion, inclination, or purpose, etc.; not firm; unsteady; fickle; changeable; variable; -- said of persons or things; as, inconstant in love or friendship.(adjective)

  source: webster1913