Capricious
Etymology
From Italian capriccio, "a sudden start, whim," which passed into English via French caprice. The origin of capriccio is disputed: it is often traced to capra, "goat," suggesting skittish, leaping behavior, but many scholars derive it instead from capo, "head," and riccio, "hedgehog" — a "hedgehog head," hair standing on end with a shudder of fright. Either way, English settled on the sense of unpredictable, whimsical impulse.
adjective · /kuh-PREE-shus/
Given to sudden, unpredictable changes of mood or behavior.
What it names
The quality of shifting on a whim, with no discernible reason — the erratic changeability of someone or something you can’t count on.
Example
The funding was capricious, generous one quarter and gone the next, so no one could plan a thing.
Related idea
Fickle stresses disloyalty and shifting affections; capricious emphasizes the sheer unpredictability of the changes, driven by whim.