bottle opener vs opener

bottle opener and opener both are nouns.

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

As nouns, opener is a hypernym of bottle opener; that is, opener is a word with a broader meaning than bottle opener:

bottle opener (noun)	opener (noun)
an opener for removing caps or corks from bottles	a hand tool used for opening sealed containers (bottles or cans)
	the first event in a series
	a person who unfastens or unwraps or opens