- arewal machine
- argentometer
- argilla
- argillaceous limestone
- argillaceous rock
- argillite argillite
- argument
- argument list
- arid
- arid ground
- aridity
- arithmetic
- arithmetic check
- arithmetic instruction
- arithmetic organ
- arithmetic processor
- arithmetic shift
- arkose
- arm mixer
- armature coil
- armature gap
- armature reaction
- armed
- armor
- armor-plate
- armored cord
- armour
- armoured concrete
- armoured hose
- aromatic hydrocarbon
- around
- array boundary
- array declarator
- array name
- array segment
- arrested anticline
- arrester
- arris
- arrisways
- arrive
- arrow key
- arrow shaped
- arroyo
- art
- arteria anonyma
- arterial
- arterial street
- artery
- artesian flow
- artful
- articulated
- articulated joint
- articulated structure
- articulation
- artifice
- artificial
- artificial cognition
- artificial dentition
- artificial environment
- artificial leather
- artificial line
- artificial magnets
- artificial stone
- artificial tooth
- artificial ventilation
- artless
- aseismic section
- ash determination
- ash removal
- ash-box
- ashlar brick
- ashore
- ashy grey
- askew
- aspect ratio
- asphalt content
- asphalt heater
- asphalt paper
- asphalt plant
- asphalt spreader
- asphalt tar
- asphaltum
- aspirail
- aspirating chamber
- aspiration chamber
- aspirator valve
- assay curve
- assaying
- assembler language
- assembling jack
- assembling stand
- assembly cooler
- assembly diagram
- assembly listing
- assembly program
- assembly time
- assignment operator
- assistance
- associate matrix
- association