Wæl-regn

According to the Old English Dictionary:

es;

wæl-regn

m. A deadly rain (the rain that caused the Flood) :-- Ic on andwlítan sígan lǽte wællregn ufan wídre eorðan; fǽhðe ic wille on weras stǽlan, and mid wǽgþreáte eall ácwellan, Cd. Th. 81, 24; Gen. 1350. wæl-regn