Cite the scanned version of the original dicionary like this:
Toller, T. Northcote, and Joseph Bosworth. "under-þeów." An Anglo-Saxon Dictionary: Based on the Manuscript Collections of the Late Joseph Bosworth : Supplement. Oxford: Clarendon Press, 1921. 733.
, es, m. One reduced to slavery, one who serves under or is subject to another, a slave, servant :-- Hé geniédde Arhalaus ðone látteów ðæt hé wæs his underþeów, Ors. 5, 11; Swt. 238, 2. Ða burgware bǽdon ðæt hié mósten beón hiera underþeówas ðá hí hié bewerian ne mehton petentes, ut quos belli clades reliquos fecit, saltem servire liceat, 4, 13; Swt. 212, 5: 2, 8; Swt. 92, 23. Ealle wurdon Iuliuse underþeówas Caesar omnes ad deditionem compulit, 5, 12, Swt. 242, 27.