kaprico

Kaprico is a sudden unreasoned want, the kind that changes a plan for no better reason than that it can. The plural does most of the work in practice: la kapricoj de la reĝo is a standard way to describe rule by mood rather than by law.

And here is the trap. Esperanto has kapro, a goat, and it has the suffix -ic- in chemistry. A tidy-minded learner assembles kapr plus ico and concludes that a whim is a goatish thing. The morphology is a fiction: kaprico is one borrowed root, and no part of it can be swapped out. Say kapra and you get goatish; say kaprica and you get capricious; the two words have no shared piece even though they share four letters.

What makes this one properly interesting is that the history half-supports the false seam. One respectable account of Italian capriccio really does route through capra, the goat, and its leaping, which is where English caper and capriole come from. The other, now the mainstream reading, takes it from capo and riccio, a bristling head. So the goats may genuinely be in there historically and are certainly not in there grammatically. This is the same class as inspiri, where the etymology tells a story the word-building rules do not.