Main entry: mercurial, erratic, fickle, quicksilver
Definition: liable to sudden unpredictable change
Usage: erratic behavior; fickle weather; mercurial twists of temperament; a quicksilver character, cool and willful at one moment, utterly fragile the next
Definition: marked by erratic changeableness in affections or attachments
Usage: fickle friends; a flirt's volatile affections