mouth
I
 /ˈmaʊθ/  noun  ,  pl   mouths /ˈmaʊðz/
  1 : the opening through which food passes into the body : the part of the face that includes the lips and the opening behind them
   [  count  ] He kissed her on the mouth.
    He threatened to punch me in the mouth.
    She stood there with her mouth agape/open.
    I burned the roof of my mouth.
    They told him to keep his mouth closed when chewing and not to talk with his mouth full.
    He wiped his mouth with a napkin after eating.
    She regretted saying it as soon as the words were out of her mouth.
    The smell of the food made my mouth water.
    The candy melts in your mouth.
    He says something stupid every time he opens his mouth. [=every time he speaks]
    The experience left a bad taste in my mouth. [=the experience left me feeling bad or disgusted]
   [  noncount  ] The medication is taken by mouth.
  2 [  count  ] : an opening in something
  — usually + of
   the mouth of a cave/bottle
  see also goal mouth
  3 [  count  ] : the place where a river enters the ocean
   the mouth of the river = the river's mouth
  4 [  singular  ] informal : an unpleasant or offensive way of talking
   That guy has quite a mouth on him.
   He has a loud mouth.
   He cursed and his mother angrily told him to watch his mouth. [=to not use offensive language]
  — see also big mouth, loudmouth, smart-mouth
  all mouth (and no trousers/action)
    Brit    informal   — used to describe someone who talks a lot about doing something but never actually does it
  born with a silver spoon in your mouth — see born
  butter wouldn't melt in someone's mouth — see butter, 1
  by word of mouth — see word, 1
  down in the mouth
   : unhappy or depressed
    I was surprised to see her looking so down in the mouth.
  foam at the mouth — see foam, 2
  from the horse's mouth — see horse, 1
  froth at the mouth — see froth, 2
  hand to mouth — see hand, 1
  heart in your mouth — see heart
  keep your mouth shut
   1 : to not say anything
    When he starts talking about politics, I just keep my mouth shut.
   2 : to not talk about something (such as a secret)
    She told me to keep my mouth shut about the news. [=she told me not to tell anyone about the news]
    I never tell him anything important because he doesn't know how to keep his mouth shut. [=he tells other people what he has been told]
  look a gift horse in the mouth — see horse, 1
  melt in your mouth — see melt, 1
  mouth to feed
   : a person (such as a child) who needs to be fed
    They can't afford another child. They already have too many (hungry) mouths to feed.
  put words in/into someone's mouth — see word, 1
  put your foot in your mouth — see foot, 1
  put your money where your mouth is — see money
  run your mouth — see run, 1
  shoot your mouth off — see shoot, 1
  shut your mouth — see shut, 1
  take the words right out of someone's mouth — see word, 1
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II
 /ˈmaʊð/  verb  , mouths, mouthed, mouth·ing [  + obj  ]
  1 : to say or repeat (something) without really meaning it or understanding it
   She was just mouthing the usual meaningless platitudes about the need for reform.
  2 : to form (words) with your lips without speaking
   The librarian mouthed “quiet.”
   silently mouthing the words to a song
  mouth off [  phrasal verb  ]
     informal   : to talk in a loud, unpleasant, or rude way
    He got in trouble again for mouthing off to his teacher.
    She's always mouthing off about how much better she could run the company herself.