Capricious /kəˈprēSHəs/ adj. 

Definition: Capricious is used to describe something characterized by its unpredictable nature, determined by chance or whim. It can also be used to describe a person and their actions. It was adapted from the 17th-century French capricieux (whimsical) — ultimately derived from the Italian capriccioso. 

Etymology: Capricious is a word of uncertain origin. Some speculations starting from the 19th century indicate that it could be connected to the portmanteau capo (“head”) + riccio (“hedgehog”), an allusion to a person shivering in fear, akin to a hedgehog.

The noun form, caprice, is attested to have appeared in the English language during the 17th century. The adjective capricious likely predates the noun by 60 years.

In a Sentence

Some believe that her capricious behavior stems from her childhood, but I know for a fact that’s not the case.

The current economic climate is as capricious as British weather — you never know what tomorrow will bring.

Why are you acting so capricious? We made plans a long time ago!

Synonyms 

Fickle, Volatile

Antonyms 

Constant, Stable