Definify.com
Webster 1913 Edition
Dun
Dun
,Verb.
 T.
 To cure, as codfish, in a particular manner, by laying them, after salting, in a pile in a dark place, covered with salt grass or some like substance. 
 Dun
(dŭn)
, Verb.
 T.
 & I.
 [
imp. & p. p. 
Dunned 
(dŭnd)
; p. pr. & vb. n. 
Dunning 
(dŭn′nĭng)
.] [AS. 
dyne 
noise, dynian 
to make a noise, or fr. Icel. dynr
, duna
, noise, thunder, duna 
to thunder; the same word as E. din
. √74. See Din
.] To ask or beset (e.g., a debtor), for payment; to urge importunately. 
Hath she sent so soon to 
 dun
? Swift.
Dun
,Noun.
 1. 
One who duns; a dunner. 
To be pulled by the sleeve by some rascally 
dun
. Arbuthnot.
2. 
An urgent request or demand of payment; 
 as, he sent his debtor a 
. dun
Dun
,Adj.
 [AS. 
dunn
, of Celtic origin; cf. W. dwn
, Ir. & Gael. donn
.] Of a dark color; of a color partaking of a brown and black; of a dull brown color; swarthy. 
Summer’s 
dun 
cloud comes thundering up.  Pierpont.
Chill and 
Falls on the moor the brief November day.
dun
Falls on the moor the brief November day.
Keble.
Dun crow 
(Zool.)
, the hooded crow; – so called from its color; – also called 
– hoody
, and hoddy
. Dun diver 
(Zool.)
, the goosander or merganser.
 Webster 1828 Edition
Dun
DUN
,Adj.
 1.
 Of a dark color; of a color partaking of a brown and black; of a dull brown color; swarthy.2.
 Dark; gloomy.In the dun air sublime.
DUN
,Verb.
T.
 DUN
,Verb.
T.
 1.
 Literally, to clamor for payment of a debt. Hence, to urge for payment; to demand a debt in a pressing manner; to urge for payment with importunity. But in common usage, dun is often used in a milder sense, and signifies to call for, or ask for payment.2.
 To urge importunately, in a general sense, but not an elegant word.DUN
,Noun.
 1.
 An importunate creditor who urges for payment.2.
 An urgent request or demand of payment in writing; as, he sent his debtor a dun.3.
 An eminence or mound. [See Down and Town.]