Cite the scanned version of the original dicionary like this:
Bosworth, Joseph. "ymen-sang." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth. Ed. Thomas Northcote Toller. Oxford: Clarendon Press, 1898. 13.
.Substitute :-- Ðé gedafenað ymensong (hymnus), Ps. Vos. 64, 2. Ymensong singað ús of songum Sione hymnum cantate nobis de canticis Sion, 136, 3 : 118, 171, Hé Gode þancode on ymensangum (ymnum, v. l. hymnis), Gr. D. 169, 12.