notional vs imaginary

notional is not a noun while imaginary is a noun.

Word	Noun	Adjective	Verb	Adverb
notional	No	Yes	No	No
imaginary	Yes	Yes	No	No

As adjectives, notional and imaginary are synonyms defined as:

notional and imaginary: not based on fact; existing only in the imagination

Other synonyms of notional include fanciful.

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

notional (adjective)	imaginary (adjective)
being of the nature of a notion or concept	not based on fact; existing only in the imagination
indulging in or influenced by fancy
not based on fact or investigation
not based on fact; existing only in the imagination