Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "plúme." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 68.
, an; f. A plum (fruit or tree) :-- Seó plúme hoc prunum, Ælfc. Gr. 6; Som. 5, 60. Plumae prunus, Txts. 88, 822 : plumum, 87, 1600. [Prompt. Parv. plowme prunum : Icel. plóma: M. H. Ger. pflúme. From Latin.] v. plýme, plúm-treów.