Source : Webster's Revised Unabridged Dictionary (1913)

Dunner \Dun"ner\, n. [From {Dun} to ask payment from.]
   One employed in soliciting the payment of debts.

Source : WordNet®

dun
     adj : of a dull grayish brown to brownish gray color; "the dun and
           dreary prairie"
     [also: {dunning}, {dunned}, {dunnest}, {dunner}]

dun
     v 1: treat cruelly; "The children tormented the stuttering
          teacher" [syn: {torment}, {rag}, {bedevil}, {crucify}, {frustrate}]
     2: persistently ask for overdue payment; "The grocer dunned his
        customers every day by telephone"
     3: cure by salting; "dun codfish"
     4: make a dun color
     [also: {dunning}, {dunned}, {dunnest}, {dunner}]

dun
     n 1: horse of a dull brownish gray color
     2: a color varying around light grayish brown; "she wore a dun
        raincoat" [syn: {grayish brown}, {greyish brown}, {fawn}]
     [also: {dunning}, {dunned}, {dunnest}, {dunner}]

dunner
     See {dun}