nail down vs narrow down

nail down and narrow down both are verbs.

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

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

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

nail down (verb)	narrow down (verb)
make final; put the last touches on; put into final form	become more focused on an area of activity or field of study
define clearly	define clearly
succeed in obtaining a position