China 
Africa 
- Automorphism group
- Automorphisms
- Automotive aerodynamics
- Automotive air conditioning
- Automotive design
- Automotive electronics
- Automotive engine
- Automotive engineering
- Automotive lighting
- Autonomic computing
- Autonomic nervous system
- Autonomous
- Autonomous agents
- Autonomous aircraft
- Autonomous robots
- Autonomous systems
- Autonomous vehicles
- Autonomy
- Autophagosome
- Autophagy
- Autophosphorylation
- Autopilot
- Autopoiesis
- Autoprotolysis
- Autopsy
- Autoradiography
- Autoreceptors
- Autoregressive
- Autoregressive conditional heteroskedasticity
- Autoregressive fractionally integrated moving average
- Autoregressive integrated moving average
- Autoregressive model
- Autoregressive moving-average model
- Autoregulation
- Autorotation
- Autosampler
- Autoscaling
- Autosomal
- Autosomal recessive
- Autosomes
- Autostereoscopic
- Autotaxin
- Autothrottle
- Autotransformer
- Autotransfusion
- Autoxidation
- Autunite
- Auxetic
- Auxiliary electrode
- Auxiliary feedwater
- Auxiliary field
- Auxiliary particle filter
- Auxiliary power
- Auxochrome
- Auxostat
- Auxotrophic
- Auxotrophy
- Availability
- Availability factor
- Availability heuristic
- Availability-based tariff
- Available light
- Available water capacity
- Avalanche breakdown
- Avalanche diode
- Avalanche effect
- Avalanche photodiode
- Avalanches
- Avatars
- Avenues
- Average
- Average absolute deviation
- Average fixed cost
- Average path length
- Average-case complexity
- Averages
- Avermectin
- Avgas
- Aviation English
- Aviation biofuel
- Aviation fuel
- Aviation insurance
- Aviation safety
- Aviation safety reporting system
- Avidin
- Avidity
- Avionics full-duplex switched ethernet
- Avionics software
- Avobenzone
- Avoidance coping
- Avoided burden
- Avrami equation
- Avulsion
- Avulsion fracture
- Awaruite
- Axenic
- Axial chirality
- Axial compressor
- Axial current
- Axial flux motors
- Axial piston pump
- Axial ratio
- Axial skeleton
- Axial symmetry
- Axial turbines
- Axial-flow pump
- Axicon
- Axillary
- Axillary artery
- Axillary lymph nodes
- Axillary nerve
- Axillary vein
- Axinite
- Axiom
- Axiom of extensionality
- Axiom schema
- Axiomatic design
- Axiomatic system
- Axis
- Axis of rotation
- Axis of symmetry
- Axle
- Axon guidance
- Axon hillock
- Axon terminal
- Axonal
- Axonal transport
- Axonometric projection
- Axoplasm
- Aza-
- Aza-cope rearrangement
- Azathioprine
- Azelaic acid
- Azeotropic
- Azide
- Azimuth
- Azimuth thrusters
- Azimuthal quantum number
- Aziridine
- Aziridines
- Azo compounds
- Azo coupling
- Azo dyes
- Azobenzene
- Azobisisobutyronitrile
- Azodicarbonamide
- Azoles
- Azores High
- Azospirillum brasilense
- Azotobacter chroococcum