sea-coast vs seaside

sea-coast and seaside both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea-coast	Yes	No	No	No
seaside	Yes	No	No	No

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

Other hyponyms of sea-coast include litoral, littoral, littoral zone, sands, landfall, seaboard, tideland.

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