hydroplane vs airplane

hydroplane and airplane both are nouns.

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

As nouns, airplane is a hypernym of hydroplane; that is, airplane is a word with a broader meaning than hydroplane:

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

Other hypernyms of hydroplane include aeroplane, plane.

hydroplane (noun)	airplane (noun)
an airplane that can land on or take off from water	an aircraft that has a fixed wing and is powered by propellers or jets
a speedboat that is equipped with winglike structures that lift it so that it skims the water at high speeds

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