denu
This might be just a supplemental entry adding to an entry in the Main Volume.
Related §§ in Wright's OE Grammar:
In the OE text, the length is:indicated by acute accentsindicated by macronsnot indicated.
denu
AddEalle men fleód tó muntum and tó denum (in speluncas montium ) hié tó behýdanne, and hié cweðað: 'Wé hálsiað eów, muntas and dena, gé ús oferfeallen,' Verc. Först. 108, 11. v. feld-denu, fild-denu, mearc-denu, stán-denu.
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.

Abbreviation not recognized. See:

A Combined List of Abbreviations.