tie down vs tie

tie down is not a noun while tie is a noun.

Word	Noun	Adjective	Verb	Adverb
tie down	No	No	Yes	No
tie	Yes	No	Yes	No

tie down (noun)	tie (noun)
	a cord (or string or ribbon or wire etc.) with which something is tied
	neckwear consisting of a long narrow piece of material worn (mostly by men) under a collar and tied in knot at the front
	a horizontal beam used to prevent two other structural members from spreading apart or separating
	one of the cross braces that support the rails on a railway track
	a fastener that serves to join or connect
	(music) a slur over two notes of the same pitch; indicates that the note is to be sustained for their combined time value
	the finish of a contest in which the score is tied and the winner is undecided
	equality of score in a contest
	a social or business relationship

tie down (verb)	tie (verb)
restrain from independence by an obligation	form a knot or bow in
secure with or as if with ropes	limit or restrict to
	finish a game with an equal number of points, goals, etc.
	fasten or secure with a rope, string, or cord
	connect, fasten, or put together two or more pieces
	unite musical notes by a tie
	make by tying pieces together
	perform a marriage ceremony
	create social or emotional ties