- specified temperature
- specimen
- spectral density
- spectral method
- spectral series
- spectral splitting
- spectrography
- spectrohelioscope
- spectrophotometer
- spectroprojector
- spectroscopic binary
- spectrum broadening
- specular reflector
- speculum
- speech channel
- speech tone
- speed monitor
- spherical capacitor
- sphericity
- specific loading
- specific resistance
- specimen standard
- specpure
- spectrographic
- spectrometer
- spectrometry
- speed variation
- spherical coordinates
- spherical mirror
- spherical projection
- spherical wave
- spherocylindric
- spicule
- spin glass
- spin ordering
- spin valve
- spin-space
- spinel structure
- spinner
- spinning humidifier
- spiderweb
- spiked waveform
- spin chiller
- spin echo
- spin effect
- spin flip
- spin flipping
- spine fin
- spinel ferrite
- spintherometer
- spiral filament
- spiral nebulae
- spiral scanning
- split fin
- split winding
- splitter
- spontaneous magnetization
- sporadic fault
- sporadic reflections
- spot
- spray
- spray cooling
- spray dehydration
- spray humidification
- sprayed insulation
- spread reflection
- spreading coefficient
- spring contact
- spring drive
- spring tension
- spurious emission
- spurious radiation
- sputnik
- squared shape
- squareness ratio
- squaring
- spinthariscope
- spiral fin
- spiral galaxy
- splash-proof
- split casing
- split condenser
- split fitting
- splitting factor
- sponge
- spontaneous emission
- spontaneous polarization
- spontaneous process
- spontaneous transition
- stability
- stabilization
- stabilizer
- stacked array
- stacking pattern
- stage expansion
- stagnation pressure
- stalloy
- stand-alone
- standard air
- standard atmosphere