narrow margin vs narrowness

narrow margin and narrowness both are nouns.

Word	Noun	Adjective	Verb	Adverb
narrow margin	Yes	No	No	No
narrowness	Yes	No	No	No

As nouns, narrow margin and narrowness are synonyms defined as:

Other synonyms of narrow margin include slimness.

narrow margin (noun)	narrowness (noun)
a small margin	the property of being narrow; having little width
	a small margin
	an inclination to criticize opposing opinions or shocking behavior
	a restriction of range or scope