mouthful /mowthˈfəl/ noun (pl mouthˈfuls)

1. As much food, etc as fills the mouth
2. A small quantity of food or drink
3. A big word
4. A momentous utterance (slang)
5. An outburst of strong language

mouthˈless adjective

mouthy /mowdhˈi or mowthˈi/ adjective (mouthˈier; mouthˈiest)

1. Ranting
2. Inclined to backchat, cheeky (informal)
3. Affectedly over-emphatic

mouthbreather /mowthˈbrē-dhər/ noun

A person who habitually breathes through the mouth

mouthˈbreeder or mouthˈbrooder noun

A cichlid fish that carries its young in its mouth for protection

mouthˈfeel noun

The sensory perception of a particular food while chewed, etc in the mouth

mouth-filling /mowthˈ/ adjective

Full-sounding

mouthˈ-friend noun (Shakespeare)

A person who only professes friendship

mouth harp noun

A mouth organ

mouthˈ-honour noun (Shakespeare)

Insincere civility

mouthˈ-made adjective (Shakespeare)

Insincere

mouth music noun

Music (usu accompanying dance) sung, not played on or accompanied by instrument(s)

mouth organ noun

1. A small musical instrument encasing metallic reeds, played by the mouth, a harmonicon or harmonica
2. Pan-pipes

mouthˈparts plural noun

Any of the limblike parts adapted for feeding that surround the mouth of an arthropod

mouthˈpiece noun

1. The piece of a musical instrument, tobacco pipe, mask, etc held to or in the mouth
2. A cigarette holder
3. A gumshield
4. A spokesman or spokeswoman

mouth-to-mouthˈ adjective

Designating a method of artificial respiration in which a person breathes air directly into the patient's mouth to inflate the lungs

mouthˈwash noun

1. An antiseptic solution for cleansing the mouth and for gargling with
2. Rubbish, nonsense (informal)

mouthˈwatering adjective

Causing the release of saliva in the mouth, highly appetizing (also figurative)

be all mouth (slang)

To be unable to support one's boastful talk with action

by word of mouth see under word

down in the mouth see under down¹

have a big mouth (informal)

To (habitually) talk indiscreetly, loudly, or too much

keep one's mouth shut (informal)

Not to divulge a secret, etc

make a poor mouth

To profess poverty

mouth off (slang, esp US)

1. To express one's opinions forcefully and loudly, sound off
2. To boast, brag

shoot one's mouth off (slang)

To talk freely, inaccurately, tactlessly, etc

shut or stop the mouth of

To silence

watch one's mouth (informal)

To be careful not to be indiscreet