pin down vs narrow down

pin down and narrow down both are verbs.

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

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

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

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