standstill vs stand still

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

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

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

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