[duhn] 
verb, dunned, dun⋅ning, noun | 1. | to make repeated and insistent demands upon, esp. for the payment of a debt. |
| 2. | a person, esp. a creditor, who duns another. |
| 3. | a demand for payment, esp. a written one. |
| dun 1 (dŭn) tr.v. dunned, dun·ning, duns To importune (a debtor) for payment: a dunning letter. n.
[Origin unknown.] |
| dun 2 (dŭn) n.
[Middle English, from Old English dunn, perhaps of Celtic origin.] |