Hippocampus vs sea horse

Hippocampus and sea horse both are nouns.

Word	Noun	Adjective	Verb	Adverb
Hippocampus	Yes	No	No	No
sea horse	Yes	No	No	No

Hippocampus (noun)	sea horse (noun)
seahorses	small fish with horse-like heads bent sharply downward and curled tails; swim in upright position
	either of two large northern marine mammals having ivory tusks and tough hide over thick blubber