Synonyms: 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
Similar words: changeable, changeful
Definition: such that alteration is possible; having a marked tendency to change
Usage: changeable behavior; changeable moods; changeable prices
Definition: marked by erratic changeableness in affections or attachments
Usage: fickle friends; a flirt's volatile affections
Similar words: inconstant
Definition: likely to change frequently often without apparent or cogent reason; variable
Usage: inconstant affections; an inconstant lover; swear not by...the inconstant moon- Shakespeare