Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "lang-ness." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 606.
, e; f. Length :-- Brádnyss langnyss heáhnyss and deópnyss breadth, length, height and depth, Homl. Th. ii. 408, 21. Langnysse dagena ic gefylle hine longitudine dierum replebo eum, Ps. Spl. 90, 16. Ðonne sceal man ðysne wyrttruman gedrígean and ða langnysse tóceorfan on pysena gelícnysse this plant is to be dried, and its length cut up into pieces about the size of peas, Herb. 140, 1; Lchdm. i. 260, 15. Ealle óðre dagas on twelf mónþum habbaþ mislíce langnisse all other days in the twelve months have various lengths, Lchdm. iii. 258, 2.