erratic

Synonyms: aberrant abnormal anomalous arbitrary bizarre capricious changeable desultory devious dicey directionless dubious eccentric fitful flaky fluctuant idiosyncratic iffy incalculable inconsistent inconstant irregular meandering mercurial nomadic oddball peculiar planetary rambling roving shifting spasmodic strange stray uncertain undirected unnatural unreliable unstable unusual vagarious variable volatile wayward weird whimsical

Antonyms: certain consistent definite dependable predictable regular reliable steady sure unchanging