fossil oil vs oil

fossil oil and oil both are nouns.

Word	Noun	Adjective	Verb	Adverb
fossil oil	Yes	No	No	No
oil	Yes	No	Yes	No

As nouns, fossil oil and oil are synonyms defined as:

Other synonyms of fossil oil include crude, crude oil, petroleum, rock oil.

As nouns, oil is a hypernym of fossil oil; that is, oil is a word with a broader meaning than fossil oil:

fossil oil: a dark oil consisting mainly of hydrocarbons
oil: a slippery or viscous liquid or liquefiable substance not miscible with water

Other hypernyms of fossil oil include fossil fuel.

fossil oil (noun)	oil (noun)
a dark oil consisting mainly of hydrocarbons	oil paint containing pigment that is used by an artist
	any of a group of liquid edible fats that are obtained from plants
	a slippery or viscous liquid or liquefiable substance not miscible with water
	a dark oil consisting mainly of hydrocarbons

fossil oil (verb)	oil (verb)
	administer an oil or ointment to; often in a religious ceremony of blessing
	cover with oil, as if by rubbing