(dun) v.t. & v.i. dunned, dun·ning
To press (a debtor) for payment; importune; pester.
—noun
1. One who duns.
2. A demand for payment. [Prob. var. of DIN¹]

(dun) adjective
Of a grayish–brown or reddish–brown color.
—noun
1. Dun color.
2. A dun–colored horse.
3. Obs. A nickname for an old horse; a jade.
4. A dun fly.
—v.t. dunned, dun·ning
1. To make dun–colored.
2. U.S. To cure (fish) by salting and packing in a dark place. [OE dunn]

(dun) noun
In ancient Ireland and Scotland, a fort or fortified dwelling, encircled by earthworks or mounds: surviving in place names, as Dundalk, Dundee, etc. [<Irish dūn hill]