broyer

To grind, crush, or pulverize — broyer du grain, un broyeur à déchets — and, in the well-known fixed expression broyer du noir, to feel deeply down or depressed.

• Le moulin broie le grain en farine. — The mill grinds grain into flour.
• Depuis son licenciement, il broie du noir. — Since he was laid off, he's been feeling really down.
• Cette machine broie les déchets verts. — This machine shreds garden waste.

Broyer du noir specifically means 'to feel gloomy/depressed,' not literally 'to grind something black' — a learner translating it literally will miss the idiom entirely.

• expression "Broyer du noir" — A documented idiom whose origin traces to 16th-century painters literally grinding charred wood for dark pigment, later linked by 17th-century medicine to 'black bile' (melancholy), and settled into its modern figurative sense by the 19th century.