narrow down vs pin down

narrow down and pin down both are verbs.

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

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

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

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