Capricious

adjective/kuh-prish-us/

Meaning

given to sudden and unaccountable changes of mood or behavior.

In context
His capricious nature made him a difficult friend.

Remember it

CapriCIOUS like a leaping goat (capra) — moods that spring any direction without warning.

Use it well

For changeable weather, referees and moods: 'capricious weather'; implies unfairness or whim.