stand still vs standstill

stand still is not a noun while standstill is a noun.

Word	Noun	Adjective	Verb	Adverb
stand still	No	No	Yes	No
standstill	Yes	No	No	No

stand still (noun)	standstill (noun)
	an interruption of normal activity
	a situation in which no progress can be made or no advancement is possible

stand still (verb)	standstill (verb)
remain in place; hold still; remain fixed or immobile