big, cavernous, enormous, huge, large, wide
small, tiny
beautiful, perfect, pretty, rosebud, sensual, sensuous
red
firm, hard, strong
A smile played around his strong mouth.

soft
hot, warm
slack
full
lipless, thin
toothless
wet
dry, tight
A tight mouth was the only sign of her nerves.

gaping, half-open, open
closed
smiling
hungry
She has four hungry mouths to feed.

sore, swollen

open
clamp shut, close, shut, snap shut
cover
He covered his mouth to hide his yawn.

cup, gag
Suddenly a hand cupped her mouth.

wipe
He wiped his greasy mouth on his sleeve.

rinse, rinse out, wash out
The dentist told him to rinse his mouth out.

fill, stuff
He coughed as the blood filled his mouth.
He began to stuff his mouth with pasta.

foam at, froth at
The dog was foaming at the mouth and near death.

burn
The hot coffee burned her mouth.

kiss
purse

drop, drop open, fall open, gape, hang open, open, sag open
Our mouths dropped open in surprise.

widen
His mouth widened to a smile.

close, shut
clamp shut, snap shut
be contorted, be set, compress, contort, harden, purse, set, tighten, turn down, twist
His mouth compressed into a thin, hard line.
‘Get out!’ she shouted, her mouth contorted by emotion.
Her mouth suddenly set in a determined line.

curl, curve, lift, quirk (esp. AmE), stretch, tilt, turn up
Her mouth curved into a smile.
His mouth lifted in a wry smile.

droop, sag
pout
twitch
quiver, tremble
water
My mouth started watering when I smelled the food.

be dry, go dry
taste like sth

sore, ulcer (BrE)
cancer
care (esp. AmE)
Good mouth care is very important when you are having chemotherapy.

rinse

around your mouth
There were lines of tension around his mouth.

across your mouth
A cool smile played across her mouth.

in your mouth
I could taste blood in my mouth.

over your mouth
She put her hand over her mouth to stifle the cough.

the back of the mouth, the roof of the mouth
I was so thirsty my tongue was sticking to the roof of my mouth.

the corner of the mouth, the side of the mouth
There was blood trickling from the corner of his mouth.
The corners of her mouth turned up in a slight smile.

keep your mouth shut (= don't speak)
(have) your mouth full (= full of food)
Don't talk with your mouth full!

a mouth to feed
Twins would mean two extra mouths to feed.

Mouth is used with these nouns as the object:
lyrics, swear word, word