residual oil vs oil

residual oil and oil both are nouns.

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

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

Other hypernyms of residual oil include crude, crude oil, fossil oil, petroleum, rock oil.

residual oil (noun)	oil (noun)
oil products that remain after petroleum has been distilled	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

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