runoff vs run off

runoff is a noun but run off is not a noun.

Word	Noun	Adjective	Verb	Adverb
runoff	Yes	No	No	No
run off	No	No	Yes	No

runoff (noun)	run off (noun)
a final election to resolve an earlier election that did not produce a winner
the occurrence of surplus liquid (as water) exceeding the limit or capacity

runoff (verb)	run off (verb)
	decide (a contest or competition) by a runoff
	reproduce by xerography
	force to go away; used both with concrete and metaphoric meanings
	leave suddenly and as if in a hurry
	run away; usually includes taking something or somebody along
	run away secretly with one's beloved
	run off as waste