- Sacred cow
- Safe as houses
- Safe pair of hands
- Safe sex
- Sailing close to the wind
- Salad days
- Salt of the earth
- San fairy Ann
- Sandwich short of a picnic
- Save face
- Save one's bacon
- Saved by the bell
- Savoir faire
- Say cheese
- Say goodnight Gracie
- Scapegoat
- Scarper
- Scot-free
- Scott
- Scraping the barrel
- Screw your courage to the sticking place
- 'Scuse me while I kiss this guy
- Sea change
- Sealed with a loving kiss
- Season of mists and mellow fruitfulness
- second fiddle
- Second-guess
- Security blanket
- See a man about a dog
- See a pin and pick it up, all the day you'll have good luck; see a pin and let it lie, bad luck you'll have all day
- See red
- See the wood for the trees
- Selling like hot cakes
- Seek and you shall find
- Seen better days
- Send packing
- Senior citizen
- Sent to Coventry
- Separate the sheep from the goats
- Set one's cap at
- Set your teeth on edge
- Sex and shopping
- Seven-year itch
- Sexton Blake
- Shebang
- Shaggy dog story
- Shake a leg
- Shakers and movers
- Phrases coined by William Shakespeare
- Words coined by William Shakespeare
- Shall I compare thee to a summer's day?
- Shambles
- Shanks' mare/shanks' pony
- Share and share alike
- Shilly-shally
- Ship shape and Bristol fashion
- S*** end of the stick
- S*** for brains
- Shiver my timbers
- Shoddy
- Shoemaker always wears the worst shoes
- Shoot through
- Short end of the stick
- Short shrift
- Shot across the bows
- Shot heard 'round the world
- Shot in the arm
- Shot in the dark
- Show a leg
- Show your mettle
- Shrinking violet
- Shuffle off this mortal coil
- Shut your cake-hole
- Siamese twins
- Sick as a parrot
- Sick puppy
- Sight for sore eyes
- Similes
- Silence is golden
- Silly Billy
- Silly season
- Silver bullet
- Silver lining
- Silver spoon
- A list of 200 'As X as Y' Similes
- Sir Walter Scott
- Sitting pretty
- Six ways to Sunday
- Sixes and sevens
- Skeleton in the closet
- Skid row
- Skin and blister
- skin of your teeth
- sky's the limit
- Sledgehammer to crack a nut
- Sleep like a top
- Sleep on a clothesline
- Sleep tight
- Sleeveless errand
- Sloane Ranger
- Slogans which have become commonplace phrases
- Slush fund
- Smallest room in the house
- Smart casual
- Smoke and mirrors
- Snug as a bug in a rug
- So sue me
- Soap-dodger
- Sod's Law
- Sold down the river
- Some are born great, some achieve greatness, and some have greatness thrust upon 'em
- Some men are born mediocre, some men achieve mediocrity, and some men, have mediocrity thrust upon them
- Someone is walking over my grave
- Something for the weekend sir?
- Something nasty in the woodshed
- Something old, something new, something borrowed, something blue
- Son of a bitch
- Son of a gun
- Sorry sight
- Sound bite
- Sound out
- Sour grapes
- Space, the final frontier
- Spanner in the works
- Spare the rod and spoil the child
- Speak of the Devil
- Speak softly and carry a big stick
- Special relationship
- Spelling-bee
- Spend a penny
- Spick and span
- Spill the beans
- Spin doctor
- Spirit of the staircase
- Spitting feathers
- Spitting image
- Spoonerisms
- Spring forward, fall back
- Spruce-up
- Square meal
- Squeaky bum time
- Stand and deliver
- Stand up guy
- Standing on the shoulders of giants
- Star-crossed lovers
- Stark, raving mad
- Stars and garters
- Start from scratch
- Steal a march
- Steal my thunder
- Step up to the plate
- Stick in the mud
- Stick your oar in
- Sticks and stones may break my bones
- Sticky wicket
- Stiff upper lip
- Stiffen the sinews
- Stinking rich
- Stitch in time saves nine
- Stone the crows
- Stone's throw
- Stony-hearted
- Stool pigeon
- Storm in a teacup
- Straight as a die
- Straight from the horse's mouth
- Strain at the leash
- Strait-laced
- Strait and narrow
- Stranger danger
- Stranger than fiction
- Straw that broke the camel's back
- Strike while the iron is hot
- Stuck fast
- Stuff and nonsense
- Stump up
- Such is life
- Super-duper
- Surf and turf
- Surfing the Net/surfing the Internet/surfing the Web
- Survival of the fittest
- Suspension of disbelief
- Swan song
- Sweet Fanny Adams
- Swing for you
- Swing the lead