The zifius is found in some medieval encyclopedias. It is a sea monster unlike any other animal on land or in the sea or in the air; it is entirely unique. Its head is terrifying, as is the abyss of its mouth, and its eyes are horrifying.

Zifius is sometimes translated as swordfish, but it is more likely some kind of whale.

In modern taxonomy, the genus Xiphias includes several species of swordfish.