The Collaborative International Dictionary of English v.0.48:

Dun \Dun\ (d[u^]n), v. t. & i. [imp. & p. p. Dunned (d[u^]nd);
   p. pr. & vb. n. Dunning (d[u^]n"n[i^]ng).] [AS. dyne noise,
   dynian to make a noise, or fr. Icel. dynr, duna, noise,
   thunder, duna to thunder; the same word as E. din. [root]74.
   See Din.]
   To ask or beset (e.g., a debtor), for payment; to urge
   importunately.
   [1913 Webster]

         Hath she sent so soon to dun?            --Swift.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "dunning":
   blandishment, buttonholing, cajolement, cajolery, cajoling,
   coaxing, demanding, importunate, importunateness, importunity,
   insistent, nagging, pestering, plaguing, plying, pressing,
   pressure, teasing, urgency, urgent, urging, wheedling



U.S. Gazetteer Places (2000):

Dunning, NE -- U.S. village in Nebraska
   Population (2000):    109
   Housing Units (2000): 70
   Land area (2000):     0.227089 sq. miles (0.588158 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.227089 sq. miles (0.588158 sq. km)
   FIPS code:            13960
   Located within:       Nebraska (NE), FIPS 31
   Location:             41.827721 N, 100.104090 W
   ZIP Codes (1990):     68833
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Dunning, NE
    Dunning