Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "dæg-langes." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 761.
;adv. During one day, for a day; per unam diem :-- Beo ðé stille dæglanges ðínre fyrdinge be still for a day from thy march, Homl. Th. ii. 482, 29. v. dæg-lang.