lighter vs boat

lighter and boat both are nouns.

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

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

lighter (noun)	boat (noun)
a device for lighting or igniting fuel or charges or fires	a small vessel for travel on water
a flatbottom boat for carrying heavy loads (especially on canals)	a dish (often boat-shaped) for serving gravy or sauce
a substance used to ignite or kindle a fire

lighter (verb)	boat (verb)
transport in a flatbottom boat	ride in a boat on water