imaginary number vs complex quantity

imaginary number and complex quantity both are nouns.

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

As nouns, imaginary number and complex quantity are synonyms defined as:

imaginary number and 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 synonyms of imaginary number include complex number, imaginary.

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