fickle
1. [ adjective ] marked by erratic changeableness in affections or attachments
Synonyms: volatile
Examples:

"fickle friends" "a flirt's volatile affections"

Related terms: inconstant
2. [ adjective ] liable to sudden unpredictable change
Synonyms: mercurial quicksilver erratic
Examples:

"erratic behavior" "fickle weather" "mercurial twists of temperament" "a quicksilver character, cool and willful at one moment, utterly fragile the next"

Related terms: changeable
Similar spelling:   fizzle
  fiscal
  Fickel
  fissile
  fiscally