oil vs residual oil

oil and residual oil both are nouns.

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

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

Other hyponyms of oil include resid.

oil (noun)	residual oil (noun)
oil paint containing pigment that is used by an artist	oil products that remain after petroleum has been distilled
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

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