capricious
kuh-PRISH-usadjMeaning changing suddenly and without reason
Memory hook a goat on a whim: this way, then that. The little goat leaps left, then right, then left again, for no reason at all: just a whim. Its leaping is capricious.
The capricious weather switched from sunshine to hail three times in one afternoon.
In context The king was capricious: one day he rewarded his cook with gold, and the next, for no reason anyone could see, he banished him from the kitchen.
Similar fickle, unpredictable, changeable, whimsical
Opposite steady, consistent, predictable
From Italian capriccio, “a sudden whim.”