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
Synonyms: temperamental, erratic
Definition: likely to perform unpredictably
Usage: erratic winds are the bane of a sailor; a temperamental motor; sometimes it would start and sometimes it wouldn't; that beautiful but temperamental instrument the flute- Osbert Lancaster
Similar words: undependable, unreliable
Definition: not worthy of reliance or trust
Usage: in the early 1950s computers were large and expensive and unreliable; an undependable assistant
Synonyms: erratic, planetary, wandering
Definition: having no fixed course
Usage: an erratic comet; his life followed a wandering course; a planetary vagabond