Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "beácen." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 757.
, bécen, bécn, bécun; g. beácnes; n. A BEACON, sign, token, standard; signum, significatio, typus, vexillum, portentum, miraculum; in specie de sancta cruce et de sole :-- Leóht eástan com beorht beácen light came from the east a bright beacon, Beo. Th. 1144; B. 570. He beácen onget he perceived the sign, Cd. 198; Th. 246, 33; Dan. 488. Wæs beácen boden the token was announced, Andr. Kmbl. 2403; An. 1203. Beácnes cyme the beacon's [the sun's] coming, Exon. 57b; Th. 205, 4; Ph. 107.