mouth vs opening

mouth and opening both are nouns.

Word	Noun	Adjective	Verb	Adverb
mouth	Yes	No	Yes	No
opening	Yes	Yes	No	No

As nouns, opening is a hypernym of mouth; that is, opening is a word with a broader meaning than mouth:

As nouns, opening is a hypernym of mouth; that is, opening is a word with a broader meaning than mouth:

mouth: the externally visible part of the oral cavity on the face and the system of organs surrounding the opening
opening: an aperture or hole that opens into a bodily cavity

Other hypernyms of mouth include orifice, porta.

As nouns, opening is a hypernym of mouth; that is, opening is a word with a broader meaning than mouth:

Other hypernyms of mouth include gap.

mouth (noun)	opening (noun)
the opening of a jar or bottle	a recognized sequence of moves at the beginning of a game of chess
the externally visible part of the oral cavity on the face and the system of organs surrounding the opening	the act of opening something
the opening through which food is taken in and vocalizations emerge	becoming open or being made open
an impudent or insolent rejoinder	the first of a series of actions
the point where a stream issues into a larger body of water	a vacant or unobstructed space that is man-made
an opening that resembles a mouth (as of a cave or a gorge)	an entrance equipped with a hatch; especially a passageway between decks of a ship
a person conceived as a consumer of food	an aperture or hole that opens into a bodily cavity
a spokesperson (as a lawyer)	a possible alternative
	the initial part of the introduction
	the first performance (as of a theatrical production)
	a ceremony accompanying the start of some enterprise
	an open or empty space in or between things
	opportunity especially for employment or promotion

mouth (adjective)	opening (adjective)
	first or beginning

mouth (verb)	opening (verb)
express in speech
articulate silently; form words with the lips only
touch with the mouth