fuel vs lighter

fuel and lighter both are nouns.

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

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

fuel (noun)	lighter (noun)
a substance that can be consumed to produce energy	a device for lighting or igniting fuel or charges or fires
	a flatbottom boat for carrying heavy loads (especially on canals)
	a substance used to ignite or kindle a fire

fuel (verb)	lighter (verb)
stimulate	transport in a flatbottom boat
provide with a combustible substance that provides energy
provide with fuel
take in fuel, as of a ship