undoer vs opener

undoer and opener both are nouns.

Word	Noun	Adjective	Verb	Adverb
undoer	Yes	No	No	No
opener	Yes	No	No	No

As nouns, undoer and opener are synonyms defined as:

Other synonyms of undoer include unfastener, untier.

undoer (noun)	opener (noun)
a person who destroys or ruins or lays waste to	a hand tool used for opening sealed containers (bottles or cans)
a person who unfastens or unwraps or opens	the first event in a series
a seducer who ruins a woman	a person who unfastens or unwraps or opens