| show the flag | | | |
| show who's boss | | | |
| shuffle off this mortal coil | | | |
| shut one's eyes | | | |
| shut one's face | | | |
| shut one's trap | | | |
| sick and tired | | | |
| sick at heart | | | |
| sick man | | | |
| sick to the back teeth | | | |
| side issue | | | |
| sift out | | | |
| sigh of relief | | | |
| sign in | | | |
| sign on the dotted line | | | |
| silly me | | | |
| silver screen | | | |
| silver-tongued | | | |
| sing a different tune | | | |
| sing from the same hymnbook | | | |
| sing off the same hymn sheet | | | |
| sing the same tune | | | |
| sin tax | | | |
| sit in for | | | |
| sit one's ass down | | | |
| sit right | | | |
| sitting | | | |
| six and two threes | | | |
| six-pack of rolls | | | |
| size up | | | |
| skate over | | | |
| skeleton in the closet | | | |
| skin in the game | | | |
| skip out | | | |
| skunk at a garden party | | | |
| slam dunk | | | |
| slash | | | |
| sleep camel | | | |
| sleeping giant | | | |
| sleep on | | | |
| sleep with the fishes | | | |
| slender reed | | | |
| sling one's hook | | | |
| slip into | | | |
| slippery as an eel | | | |
| slip up | | | |
| slop out | | | |
| slower than molasses | | | |
| slow study | | | |
| slug it out | | | |
| small fry | | | |
| small wonder | | | |
| smash hit | | | |
| smash up | | | |
| smell fishy | | | |
| smell of the lamp | | | |
| smell what someone is stepping in | | | |
| smoke like a chimney | | | |
| smoke the whole pack | | | |
| smooth sailing | | | |
| snap at | | | |
| snap it up | | | |
| snap to attention | | | |
| sneaking suspicion | | | |
| sneeze on the truth | | | |
| snitches get stitches | | | |
| snowball's chance in hell | | | |
| snow on the rooftop | | | |
| soaking wet | | | |
| social death | | | |
| soda jerk | | | |
| soft | | | |
| soften up | | | |
| soft shoe | | | |
| soft underbelly | | | |
| someone's goose is cooked | | | |
| some pumpkins | | | |
| sometimes a cigar is just a cigar | | | |
| song and dance | | | |
| son of Adam | | | |
| sore point | | | |
| sort oneself out | | | |
| so there | | | |
| sound asleep | | | |
| soup sandwich | | | |
| sour grapes | | | |
| sour stomach | | | |
| sow dragon's teeth | | | |
| sow the seeds of | | | |
| spanielize | | | |
| spank the monkey | | | |
| spare no effort | | | |
| spare someone the details | | | |
| spare tyre | | | |
| speak for | | | |
| speak in circles | | | |
| speak of the devil and he appears | | | |
| speak one's mind | | | |
| speak someone's language | | | |
| speak up | | | |