Dun is a dull grayish-brown color, like the coat of certain horses or the feathers of some sparrows. A dun horse has a sandy, tan-brown coat with a darker mane and tail, and often a dark stripe down its back. The color appears in nature frequently: think of the dusty brown of a rabbit's fur or the neutral tones of dried grass in late summer.

The word creates a specific impression. It's not the rich brown of chocolate or the warm brown of a wooden desk. Dun suggests something plain, modest, and earthy. When a writer describes a dun-colored landscape, they're painting a picture of muted, quiet terrain without bright colors or drama.

The word can also mean to repeatedly ask someone for money they owe. If someone duns you for payment, they keep reminding you about a debt, like getting persistent reminders about an overdue bill. This usage turns the word into a verb: to dun someone means to press them for payment.