barrier vs seawall

barrier and seawall both are nouns.

Word	Noun	Adjective	Verb	Adverb
barrier	Yes	No	No	No
seawall	Yes	No	No	No

As nouns, seawall is a hyponym of barrier; that is, seawall is a word with a more specific, narrower meaning than barrier:

barrier: a structure or object that impedes free movement
seawall: a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away

barrier (noun)	seawall (noun)
a structure or object that impedes free movement	a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away
any condition that makes it difficult to make progress or to achieve an objective
anything serving to maintain separation by obstructing vision or access