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: moody, temperamental
Definition: subject to sharply varying moods
Usage: a temperamental opera singer
Similar words: emotional
Definition: of more than usual emotion
Usage: his behavior was highly emotional