China 
Africa 
- Atomic weight
- Atomicity
- Atomism
- Atopic dermatitis
- Atorvastatin
- Atrazine
- Atrazine chlorohydrolase
- Atresia
- Atrial
- Atrial enlargement
- Atrial fibrillation
- Atrial flutter
- Atrioventricular block
- Atrioventricular node
- Atrophic gastritis
- Atrophy
- Atryn
- Attack surface
- Attack time
- Attack tree
- Attack vector
- Attention
- Attention economy
- Attenuated
- Attenuation
- Attenuation coefficient
- Attenuation length
- Attenuators
- Atterberg limits
- Attitude
- Attitude and heading reference system
- Attitude control
- Attitude indicator
- Attosecond
- Attosecond physics
- Attractor
- Attribute domain
- Attribute-based encryption
- Attributes
- Attrition
- Atypia
- Atypical antipsychotic
- Atypical hyperplasia
- Auction algorithm
- Audience response
- Audio feedback
- Audio file format
- Audio power
- Audio power amplifier
- Audio signal processing
- Audio video bridging
- Audiobooks
- Audiology
- Audiometry
- Auditory cortex
- Auditory masking
- Auditory nerve
- Auditory system
- Audits
- Auger effect
- Auger therapy
- Augite
- Augmentative and alternative communication
- Augmented cognition
- Augmented matrix
- Auralization
- Auramine
- Auranofin
- Auricle
- Auricupride
- Aurivillius phases
- Aurophilicity
- Aurora
- Auscultation
- Austempering
- Austenite
- Austenitic stainless steel
- Authenticated encryption
- Authentication
- Authentication protocol
- Authentication server
- Authigenic
- Authorization
- Autism
- Autism spectrum
- Auto rickshaws
- Auto-configuration
- AutoAI
- AutoLISP
- Autoantibodies
- Autoantibody
- Autocatalysis
- Autocatalytic
- Autoclaved aerated concrete
- Autocollimator
- Autoconf
- Autocorrelation
- Autocovariance
- Autodesk Maya
- Autodesk Revit
- Autodock
- Autoencoders
- Autofrettage
- Autogenous welding
- Autoignition temperature
- Autoimmune
- Autoimmune hepatitis
- Autoimmunity
- Autoinducer-2
- Autoinjector
- Autoionization
- Autoland
- Autologous
- Autologous chondrocyte implantation
- Autologous stem-cell transplantation
- Automata
- Automata theory
- Automated analyzers
- Automated decision support
- Automated decision-making
- Automated fiber placement
- Automated machine learning
- Automated mineralogy
- Automated mining
- Automated storage and retrieval system
- Automated theorem proving
- Automatic
- Automatic Repeat Request
- Automatic differentiation
- Automatic exposure control
- Automatic fire suppression
- Automatic generation control
- Automatic identification and data capture
- Automatic image annotation
- Automatic lathe
- Automatic lubrication
- Automatic parallelization
- Automatic sequence
- Automatic summarization
- Automatic target recognition
- Automatic transmission
- Automatic transmission fluid
- Automatic transmission system
- Automatic variables
- Automatically tuned linear algebra software
- Automaticity
- Automation
- Automation bias
- Automation surprise
- Automation technician