seashore vs tideland

seashore and tideland both are nouns.

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

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

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

seashore (noun)	tideland (noun)
the shore of a sea or ocean	land near the sea that is overflowed by the tide