narrow margin vs slimness

narrow margin and slimness both are nouns.

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

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

Other synonyms of narrow margin include narrowness.

narrow margin (noun)	slimness (noun)
a small margin	the property of an attractively thin person
	a small margin