- rheopexy
- rheostat arm
- rheostatic regulator
- ribbed radiator
- ribbon ice
- rich liquid
- Richardson effect
- ricinus oil
- residual field
- residual losses
- residual stress
- residual unbalance
- resist
- resistance drop
- resistance lamp
- resistance thermometry
- resistive magnetohydrodynamics
- resolving power
- resonance broadening
- resonance scattering
- resonant coupling
- resonant wavelength
- resonator
- rest point
- retardation coil
- retarded
- retarding potential
- retarding voltage
- retry
- return feeder
- return line
- return main
- return refrigerant
- rim ray
- ring circuit
- ring current
- ring trip
- ring valve
- ring wire
- ringback tone
- rinsing air
- ripple current
- ripple voltage
- riser duct
- Ritchey-Chretien
- RKKY coupling
- RMS value
- return signal
- revaporization
- reverse direction
- reversed image
- reverser
- reversible booster
- reversible engine
- reversing layer
- revolution counter
- rheoscope
- rheostatic control
- rheotan
- rhombohedron
- ribboned insulation
- Riblet coupler
- rich gas
- Riemann geometry
- rigid insulation
- Roberval balance
- Rochele salt
- rock cork
- rock insulation
- rock refrigeration
- rock wool
- rod
- rod electrode
- rod gap
- roentgen current
- roentgen equivalent
- roentgen rays
- roentgenmeter
- roentgenoscopy
- rolling transposition
- room calorimeter
- room conditions
- Rollin film
- room overheating
- Rosenberg starting
- rotary converter
- rotary substation
- rotating ventilator
- rotation isolator
- rotational band
- rotational state
- rotofroster
- rom
- rontgenogram
- room cooling
- room humidistat
- room temperature
- Rossby diagram
- rotary beam
- rotary dial