- atomic blast
- atomic bomb
- atomic constant
- atomic gas
- atomic nucleus
- atomic susceptibility
- atomization freezing
- attachment plug
- attenuation equalizer
- attenuation pad
- attenuator
- attic fan
- attractor
- audio amplifier
- audiograph
- audiometer
- audiometry
- audition
- aurum
- auto-degaussing
- auto-emission
- auto-ionization
- autocall
- autoconduction
- automatic adjuster
- automatic changeover
- audibility
- audible
- audible alarm
- audible frequency
- audible sound
- audio cassette
- audio frequency
- audio transformer
- audiogram
- Auger effect
- Auger electron
- augmentation
- aurora-borealis
- auto-feed
- autocatalysis
- autocatalytic
- automated system
- automatic controller
- automatic cutout
- automatic defrosting
- automatic dialer
- automatic freezer
- automatic compressor
- automatic control
- automatic cooling
- automatic damper
- automatic evaporation
- automatic freezing
- automatic iris
- automatic purger
- automatically controlled
- auxiliary condenser
- auxiliary contacts
- auxiliary cooling
- auxiliary fan
- auxiliary plant
- av
- availability factor
- avalanche detector
- avalanche diode
- aW
- axial flow
- axiomatic formulation
- axoid
- azeotropic fluid
- azimuth resolution
- automaticity
- automotive alternator
- autostarter
- autotransformer
- auxiliary circuit
- auxiliary ejector
- auxiliary switch
- availability
- available ton
- avalanche photodiode
- axial
- axial flux
- axial quadrupole
- axis
- ayrton shunt
- azeotropic
- azeotropic refrigerant
- B battery
- B-party
- back action
- back echo
- back flow
- back porch
- back reflection
- background activity
- background noise
- background return
- background subtraction