pipefish vs sea horse

pipefish and sea horse both are nouns.

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

As nouns, sea horse is a hyponym of pipefish; that is, sea horse is a word with a more specific, narrower meaning than pipefish:

pipefish: fish with long tubular snout and slim body covered with bony plates
sea horse: small fish with horse-like heads bent sharply downward and curled tails; swim in upright position

pipefish (noun)	sea horse (noun)
fish with long tubular snout and slim body covered with bony plates	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