For-síðian

According to the Old English Dictionary:

for-síðian

p. ode; pp. od [síðian to journey] To perish; ĭter fātāle inīre :-- Hæfde ðá forsíðod sunu Ecgþeówes Ecgtheow's son had then perished, Beo. Th. 3104, note; B. 1550. for-siðian