fickle in WordNet English dictionary

1. 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"
   erratic  fickle  mercurial  quicksilver 
   
2. marked by erratic changeableness in affections or attachments
   "fickle friends"; "a flirt's volatile affections"
   fickle  volatile