octane number vs quantity

octane number and quantity both are nouns.

Word	Noun	Adjective	Verb	Adverb
octane number	Yes	No	No	No
quantity	Yes	No	No	No

As nouns, quantity is a hypernym of octane number; that is, quantity is a word with a broader meaning than octane number:

octane number: a measure of the antiknock properties of gasoline
quantity: how much there is or how many there are of something that you can quantify

Other hypernyms of octane number include amount, measure.

octane number (noun)	quantity (noun)
a measure of the antiknock properties of gasoline	how much there is or how many there are of something that you can quantify
	an adequate or large amount
	the concept that something has a magnitude and can be represented in mathematical expressions by a constant or a variable