Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "ealdor-burh." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 167.
, -burg; gen. -burge; f. A royal city, metropolis; rēgia arx, metrŏpŏlis :-- On Cantwara byrig, seó wæs ealles his ríces ealdor-burh in civĭtāte Doruvernensi, quæ impĕrii sui tōtīus erat metrŏpŏlis. Bd. 1, 25; S. 487, 19: I. 13; S. 482, 6. Godes ealdorburg God's royal city, Exon. 114 b; Th. 441, 8; Rä. 60, 15.