dun
This might be just a supplemental entry adding to an entry in the Main Volume.
In the OE text, the length is:indicated by acute accentsindicated by macronsnot indicated.
dun
Add: , dunn Dun balidus, Wrt. Voc. ii. 125, 4. Dunn (printed dunu) natius, 62, 6. On horse dunnan sittan ferðrunge getácnað, Lch. iii. 202, 30. Ðá námon þá deófolgildan þone dunnan (dumban, v. l. ) oxan, Hml. S. 18, 112. Hyre betstan dunnan tunecan, Cht. Th. 537, 31. On ðá twégen dunne stánes ... ðone dunnan stán wiðforan ðám burggete, C. D. iii. 85, 10, 13.
This is a supplementary entry with editorial changes to an entry in the main volume of the dictionary. Look under the 'Possibly connected entries' below, or for the same headword in the list to the left.

A Combined List of Abbreviations.

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A Combined List of Abbreviations.