- ataxic
- athabascaoil sand
- atmospheric nitrogen
- atmospheric regulator
- atomic group
- atomic hydrogen
- atomic mass
- atomic spectrum
- atomic weight
- atomism
- atomized brine
- atomizer quill
- atomizing carburetor
- aracanga
- arc welding
- arctic circle
- area measurement
- arenaceous limestone
- argillaceous limestone
- argillaceous texture
- aromatization process
- arrester
- arseniferous
- articulated
- articulated joint
- artificial hypothermia
- Artinskian atage
- ash cone
- asphalt coating
- asphalt content
- asphalt deposit
- asphalt jelly
- asphalt seepage
- asphaltic limestone
- asphaltic number
- asphaltic sand
- asphaltite
- astatic system
- athrogene rock
- atmospheric change
- atmospheric pollution
- atmospheric transmittancy
- atoll
- atomic compound
- atomic frequency
- atomic orbit
- atomic spectra
- atomic volume
- attack metal
- attackable
- attapulgite
- attemperator
- attendance crew
- attendance regulation
- attenuation
- attested copy
- attrition
- auriferous pyrite
- authigenic
- autochotne mass
- autoclaving
- autogenous cutting
- autogenous welding
- autolytic
- Aturian stage
- auric
- automatic cathead
- automorphic
- autooxidation
- auxiliary engine
- auxiliary tank
- avalanche
- avalanche breccia
- average efficiency
- average hade
- average sample
- average seed
- average trend
- avocado oil
- axle load
- ayan
- azeotropic distillation
- automotive grease
- aviation fuel
- avodire
- axle oil
- axle spindle
- azeotropic
- azimino compound
- azo compound
- azotes
- azotometer
- azure
- babassu oil
- babbit lined
- baby soap
- back burning
- back digger
- back draft
- back entry