narrow down vs nail down

narrow down and nail down both are verbs.

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

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

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

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