Sǽ-deór

According to the Old English Dictionary:

es;

sǽ-deór

m. A sea-beast (cf. Milton's 'that sea-beast Leviathan'):--Hine swencte on sunde sǽdeór monig, Beo. Th. 3025; B. 1510. Hé hét his ágene men hine sændan on ðone sǽ, and ða sǽdeór hine sóna forswulgon, Shrn. 54, 27. Hý mon wearp in sǽdeóra seáþ, 133, 11. Gif hit on Frigedæig þunrige, ðæt tácnaþ sǽdeóra cwealm, Lchdm. iii. 180, 17. [Icel. sjó-dýr.] sæ-deor