Fóþorn

According to the Old English Dictionary:

fóþorn

This form seems untenable. The instrumental of the pronoun seems always þý (cf. e.g. hrín mid þý snidísene, Lch. ii. 208, 16). Some word containing þorn might be expected, cf. e.g. ælcne pocc man sceall áweg ádelfan mid þorne, 106, 3. Dr. Bradley suggests þéfeþorn. foþorn