seawall vs barrier

seawall and barrier both are nouns.

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

As nouns, barrier is a hypernym of seawall; that is, barrier is a word with a broader meaning than seawall:

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

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