asiner

An extremely rare, half-humorous literary verb meaning to behave like a donkey (âne) — stubborn, foolish, or plodding. It essentially never appears outside old or playful literary writing.

• Il asine depuis le début de la réunion. — He's been acting like a stubborn mule since the meeting started.
• Cesse d'asiner et réponds sérieusement. — Stop being an ass about it and answer seriously.
• Ce personnage asine à chaque scène du roman. — This character acts the fool in every scene of the novel.

This word is so rare that even most native speakers wouldn't recognize it — a learner will essentially never need to use it; it's here for completeness, not practical use.