capricious

Adjective

• determined by chance or impulse or whim rather than by necessity or reason
  • a capricious refusal
    
  • authoritarian rulers are frequently capricious
    
  • the victim of whimsical persecutions
    

• changeable
  • a capricious summer breeze
    
  • freakish weather
    

Related words

• Synonyms: 
  impulsive , whimsical , freakish