Sceó

According to the Old English Dictionary:

sceó

a cloud (?) :-- Scearp cymeþ sceó wið óðrum, ecg wið ecge (of the coming together of clouds charged with electricity), Exon. Th. 385, 8 ; Rä. 4, 41. [O. Sax. skio : Icel. ský a cloud.] sceo