Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "ymbren-dæg." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 753.
, es; m. An Ember-day :-- Wé forbeódaþ ordál and áðas freólsdagum and ymbrendagum, L. C. E. 17; Th. i. 370, 3: Wulfst. 117, 15. Ða ðe heora lencten wel gefæsten and ða twelf ymbrendagas, 244, 20. ¶ with riht prefixed :-- Ðis synt ða rihtymbrendagas (legitimi quatuor temporum dies), ðe man mid rihte healdan sceal; ðæt is, on kł. Martii, on ðære forman wucan; and kł. Iunii, on ðære æfteran wucan; and on kł. Septemƀ. on ðære þriddan wucan; and on kł. December, on ða néhstan wucan ǽr Cristes mæssan, L. Ecg. P. addit. 21; Th. ii. 234, 33.