Fór-syngian

According to the Old English Dictionary:

-singian;

fór-syngian

p. ode, ade; pp. od, ad [syngian to sin] To sin greatly; multum peccāre :-- Ne wurþ ǽnig man on worlde swá swíðe fórsyngad, ðe he wið Gode gebétan ne mǽge no man in the world is so very sinful, that he may not make atonement to God, L. Pen. 12; Th. ii. 282, 1. [Cf. Ger. sich versündigen to sin against.] for-syngian