Undern-sang

According to the Old English Dictionary:

es;

undern-sang

m. The service at the third hour of the day, tierce :-- Undernsang tertia, R. Ben. 39, 19: 40, 6: L. Ælfc. C. 19; Th. ii. 350, 6. Undernsanges gebed tertie oratio, R. Ben. Interl. 47, 10. Æt ǽfensonge and æt undernsonge, Chart. Th. 137, 34. undern-sang