Source : Webster's Revised Unabridged Dictionary (1913)
Sea serpent \Sea" ser`pent\
1. (Zo["o]l.) Any marine snake. See {Sea snake}.
2. (Zo["o]l.) A large marine animal of unknown nature, often
reported to have been seen at sea, but never yet captured.
Note: Many accounts of sea serpents are imaginary or
fictitious; others are greatly exaggerated and
distorted by incompetent observers; but a number have
been given by competent and trustworthy persons, which
indicate that several diverse animals have been called
sea serpents. Among these are, apparently, several
large snakelike fishes, as the oar fish, or ribbon fish
({Regalecus}), and huge conger eels. Other accounts
probably refer to the giant squids ({Architeuthis}).
Some of the best accounts seem to describe a marine
saurian, like the fossil Mosasauri, which were large
serpentlike creatures with paddles.
Source : WordNet®
sea serpent
n : huge creature of the sea resembling a snake or dragon