unfastener vs untier

unfastener and untier both are nouns.

Word	Noun	Adjective	Verb	Adverb
unfastener	Yes	No	No	No
untier	Yes	No	No	No

As nouns, unfastener and untier are synonyms defined as:

Other synonyms of unfastener include opener, undoer.

unfastener (noun)	untier (noun)
a person who unfastens or unwraps or opens	a person who unfastens or unwraps or opens