Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "ýr." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 753.
the name of the rune for y, a bow (?) :-- Ýr byð æðelinga wyn and fyrdgeatewa sum, Runic pm. Kmbl. 344, 29; Rún. 27. The letter occurs Exon. Th. 50, 14; Cri. 800: 284, 28; Jul. 704; Elen. Kmbl. 2518; El. 1260. [Icelandic has ýr; gen. ýs a yew, also a bow, as the name of the Runic y.]