sound out vs mouth

sound out is not a noun while mouth is a noun.

Word	Noun	Adjective	Verb	Adverb
sound out	No	No	Yes	No
mouth	Yes	No	Yes	No

sound out (noun)	mouth (noun)
	the opening of a jar or bottle
	the externally visible part of the oral cavity on the face and the system of organs surrounding the opening
	the opening through which food is taken in and vocalizations emerge
	an impudent or insolent rejoinder
	the point where a stream issues into a larger body of water
	an opening that resembles a mouth (as of a cave or a gorge)
	a person conceived as a consumer of food
	a spokesperson (as a lawyer)

sound out (verb)	mouth (verb)
try to learn someone's opinions and intentions	express in speech
speak, pronounce, or utter in a certain way	articulate silently; form words with the lips only
	touch with the mouth