ark vs boat

ark and boat both are nouns.

Word	Noun	Adjective	Verb	Adverb
ark	Yes	No	No	No
boat	Yes	No	Yes	No

As nouns, boat is a hypernym of ark; that is, boat is a word with a broader meaning than ark:

ark (noun)	boat (noun)
a boat built by Noah to save his family and animals from the flood	a small vessel for travel on water
	a dish (often boat-shaped) for serving gravy or sauce

ark (verb)	boat (verb)
	ride in a boat on water