- shutter
- siccative
- side echo
- siemens
- single scattering
- single step
- single-acting
- single-focusing
- single-phasing
- single-range
- singlet
- singlet state
- sink
- sidereal clock
- signal voltage
- signalling
- signalling device
- silencer
- silent period
- silica gel
- silicone
- silicone oil
- silmanal
- Silsbee effect
- silver migration
- silver solder
- silvery
- similarity
- sinor
- sintered ferrite
- sintered plate
- sintering
- sinusoidal current
- sinusoidal input
- sinusoidal signal
- siphon
- siphon barometer
- siren
- skew correction
- skew scattering
- sliding
- slug
- small calorie
- smart transducer
- smoke damper
- smoke detector
- skiagraph
- skiascop
- skin depth
- skin effect
- skin resistance
- skin tracking
- skip distance
- skip effect
- sky noise
- sky wave
- SL cable
- slab insulation
- slave clock
- slide
- smoothing circuit
- snow deposit
- snow gun
- snow removal
- sodium vapour
- soft edges
- soft ice
- soft solder
- soft steel
- software package
- slave mode
- slewing rate
- slice ice
- slide damper
- slight freezing
- slot coupling
- slow melting
- sludge formation
- slug flow
- slug tuning
- slush freezer
- small-size
- smoke tube
- sliding valve
- sline scanner
- slip
- slot radiator
- slow mode
- slow-motion
- slug tuner
- slush ice
- small compressor
- smoothing
- smoothing filter
- snail clamp
- snap gage
- snow formation
- snapshot
- snow blower
- snow crystal