Un-slæc
Bosworth & Toller Anglo-Saxon Old English Dictionary - un-slæc
According to the Old English Dictionary:
-sleac;
- un-slæc
- adj. Not slack, not lazy, strenuous, active, diligent :-- Unsleac inpiger, Wrt. Voc. ii. 47, 30: 93, 15: Kent. Gl. 140. [Icel. ú-slakr.] un-slæc