- arc furnace
- arc metal
- arc rectifier
- arc welder
- arcade
- arch bridge
- arch camber
- arch floor
- arch girder
- arch ring
- arch span
- arch stone
- arch timbering
- archaeologer
- archaic
- arched bridge
- arched dam
- arched roof
- archimedean screw
- arching horn
- architectural complex
- architecture
- archive site
- archiving
- arciform
- arctic
- arcuate
- are generator
- area chart
- area geology
- area search
- areal
- arenaceous rock
- argent
- argentum
- argillaceous
- argillaceous ground
- argillaceous sand
- argillaceous slate
- argillization
- argon laser
- argon rectifier
- arid region
- arithmetic expression
- arithmetic inspection
- arithmetic operator
- arithmetic progression
- arithmetical
- arm
- arm-chair
- armature
- armature grove
- armlet
- armored cable
- armoring
- armory
- armoured glass
- armouring
- armstrong
- arrange
- array
- array expression
- array processing
- array variable
- arresting stop
- arrissing tool
- arrival rate
- arrival time
- arrow
- arrow drill
- arsiticial precipitation
- artesian
- artesian discharge
- arthemetic progression
- arthritis
- articulated concrete
- articulation index
- artifact
- artificial abortion
- artificial asphalt
- artificial brain
- artificial cooling
- artificial denture
- arithmetic element
- arithmetic function
- arithmetic operation
- arithmetic sequence
- arithmetical progression
- arithmetics
- arm crane
- arm support
- arm-lock
- armature contact
- armored car
- arrangement
- array element
- array representation
- arrest
- arrested dune
- arresting