Fyrn-syn
Bosworth & Toller Anglo-Saxon Old English Dictionary - fyrn-syn
According to the Old English Dictionary:
-synn,
- fyrn-syn
- e; f. A sin of yore; priscum peccātum :-- Fyrnsynna fruma the author of sins of yore, Exon. 70 b; Th. 263, 9; Jul. 347. fyrn-syn