capricious
/kə-ˈpri-shəs/
adjective
governed or characterized by caprice : impulsive, unpredictable
inconstant fickle capricious mercurial unstable mean lacking firmness or steadiness (as in purpose or devotion). inconstant implies an incapacity for steadiness and an inherent tendency to change. fickle suggests unreliability because of perverse changeability and incapacity for steadfastness.