tie vs untie

tie is a noun but untie is not a noun.

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

tie (noun)	untie (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 (verb)	untie (verb)
form a knot or bow in	undo the ties of
limit or restrict to	cause to become loose
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