Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "níd-máge." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 65.
, an ; f. A near kinswoman, a cousin :-- Ǽfre ne geweorðe ðæt cristen man gewífige on ðæs wífes nýdmágan ðe hé ǽr hæfde, L. Eth. vi. 12; Th. i. 318, 16. Nédmágan, L. C. E. 7 ; Th. i. 364, 24. v. níd-mǽg.