run off vs runoff

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

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

run off (noun)	runoff (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

run off (verb)	runoff (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