Capricious: impulsive; fickle; whimsical; changeable; erratic 

The ancient gods were capricious.  They were happy one moment, and irate the next.   

Source: Capricious came to English via the French word capricieux meaning capricious, or whimsical.  In French, a whim is caprice.  Beyond that, etymologists aren’t sure.  Some guess it could have come from capra, the Latin word for goat.  Possibly a reference to the frisky nature of goats.  

Synonyms: erratic, unpredictable, arbitrary, unstable

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