touch down vs touchdown

touch down is not a noun while touchdown is a noun.

Word	Noun	Adjective	Verb	Adverb
touch down	No	No	Yes	No
touchdown	Yes	No	No	No

touch down (noun)	touchdown (noun)
	a score in American football; being in possession of the ball across the opponents' goal line
	a landing (as the wheels touch the landing field); especially of airplanes

touch down (verb)	touchdown (verb)
come or bring (a plane) to a landing