Otus and his twin Ephialtes were giants, the sons of Poseidon and Iphimedia (although actually called the Aloadae or 'sons of Alöeus' since he had been the husband of Iphimedia before she married Poseidon). Otus' name derives from otheo, 'to push', 'thrust', 'force back' (as in battle). This is a suitable name for a strong giant.