Cite the scanned version of the original dicionary like this:
Bosworth, Joseph. "gánung." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth. Ed. Thomas Northcote Toller. Oxford: Clarendon Press, 1898. 361.
.Add: opening of the mouth in scorn or abuse (? cf. Ps. Th. 108, I under gánian) :-- Gánung gannatura (cf. gannature bysmires, 85,67), Wrt. Voc. ii. 70, 30. [Ganynge oscitatus, Prompt. Parv. 185 : hiatus, Cath. Ang. 149.]