pin down vs narrow

pin down is not a noun while narrow is a noun.

Word	Noun	Adjective	Verb	Adverb
pin down	No	No	Yes	No
narrow	Yes	Yes	Yes	No

As verbs, pin down and narrow are synonyms defined as:

Other synonyms of pin down include nail down, narrow down, peg down, specify.

pin down (noun)	narrow (noun)
	a narrow strait connecting two bodies of water

pin down (adjective)	narrow (adjective)
	not wide
	very limited in degree
	lacking tolerance or flexibility or breadth of view
	characterized by painstaking care and detailed examination
	limited in extent or scope

pin down (verb)	narrow (verb)
define clearly	make or become more narrow or restricted
attach with or as if with a pin	become tight or as if tight
place in a confining or embarrassing position	become more focused on an area of activity or field of study
	define clearly