pin down vs nail down

pin down and nail down both are verbs.

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

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

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

pin down (verb)	nail down (verb)
define clearly	make final; put the last touches on; put into final form
attach with or as if with a pin	define clearly
place in a confining or embarrassing position	succeed in obtaining a position