sea serpent

an enormous, imaginary, snakelike or dragonlike marine animal.

(initial capital letters) Astronomy. the constellation Hydra.

Origin of sea serpent

First recorded in 1640–50

I believe something has killed the sea-serpent at the bottom of the sea and this is its ghost!

The Boy With the U. S. Fisheries |Francis Rolt-Wheeler
Colonel Stewart, who accompanied him, threw some light on the sea-serpent.

The Personal Life Of David Livingstone |William Garden Blaikie
It may be noted that both the Malays and the Chinese attribute the origin of ambergris to either a sea-dragon or a sea-serpent.

Mythical Monsters |Charles Gould
Somebody said that if Gunn were to model his style on Ranji's the result would be a sea-serpent—six and a half feet of curves.

The Harmsworth Magazine, v. 1, 1898-1899, No. 2 |Various

I would be scandalised being stepmother to a girl that would be swallowed by a sea-serpent!

Three Wonder Plays |Lady I. A. Gregory

sea serpent

a huge legendary creature of the sea resembling a snake or dragon