Capricious \kuh-PRISH-us\ governed or characterized by caprice : impulsive, unpredictable
The noun caprice, which first appeared in English in the mid-17th century, is a synonym of whim. Evidence shows that the adjective capricious debuted about sixty years before caprice; it's likely, however, that both words derived via French from the Italian capriccio, which originally referred not to a sudden desire but to a sudden shudder of fear. Capriccio in turn derives from the Italian capo, meaning "head,"and riccio, the word for "hedgehog." Someone who shuddered in fear, therefore, was said to have a "hedgehog head"—meaning that his or her hair stood on end like the spines of a hedgehog.