real number vs complex quantity

real number and complex quantity both are nouns.

Word	Noun	Adjective	Verb	Adverb
real number	Yes	No	No	No
complex quantity	Yes	No	No	No

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

real number: any rational or irrational number
complex quantity: (mathematics) a number of the form a+bi where a and b are real numbers and i is the square root of -1

Other hypernyms of real number include complex number, imaginary, imaginary number.

real number (noun)	complex quantity (noun)
any rational or irrational number	(mathematics) a number of the form a+bi where a and b are real numbers and i is the square root of -1