fickle

/ˈfi-kəl/

Middle English fikel deceitful, inconstant, from Old English ficol deceitful; akin to Old English befician to deceive, and probably to Old English fāh hostile

adjective

  1. marked by lack of steadfastness, constancy, or stability : given to erratic changeableness

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.