speedboat vs hydrofoil

speedboat and hydrofoil both are nouns.

Word	Noun	Adjective	Verb	Adverb
speedboat	Yes	No	No	No
hydrofoil	Yes	No	No	No

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

speedboat: a fast motorboat
hydrofoil: a speedboat that is equipped with winglike structures that lift it so that it skims the water at high speeds

Other hyponyms of speedboat include hydroplane.

speedboat (noun)	hydrofoil (noun)
a fast motorboat	a speedboat that is equipped with winglike structures that lift it so that it skims the water at high speeds
	a device consisting of a flat or curved piece (as a metal plate) so that its surface reacts to the water it is passing through