seashore vs seaside

seashore and seaside both are nouns.

Word	Noun	Adjective	Verb	Adverb
seashore	Yes	No	No	No
seaside	Yes	No	No	No

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

Other hyponyms of seashore include litoral, littoral, littoral zone, sands, landfall, seaboard, tideland.

seashore (noun)	seaside (noun)
the shore of a sea or ocean	the shore of a sea or ocean regarded as a resort