airplane vs seaplane

airplane and seaplane both are nouns.

Word	Noun	Adjective	Verb	Adverb
airplane	Yes	No	No	No
seaplane	Yes	No	Yes	No

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

airplane: an aircraft that has a fixed wing and is powered by propellers or jets
seaplane: an airplane that can land on or take off from water

airplane (noun)	seaplane (noun)
an aircraft that has a fixed wing and is powered by propellers or jets	an airplane that can land on or take off from water

airplane (verb)	seaplane (verb)
	glide on the water in a hydroplane