- approach light
- approach road
- approach sequence
- approach span
- approval
- approval test
- approve
- approved budget
- approved leave
- approximate
- approximate calculation
- approximate method
- approximate reasoning
- approximate value
- approximating
- appurtenances
- apron
- apron elevator
- apron plain
- aprosody
- apse
- aqua
- aqualung
- aqueduct bridge
- aquiferous
- arachis oil
- arbitration
- arbor
- arborescent
- arc
- arc chamber
- arc coordinate
- arc dam
- arc discharger
- arc transmitter
- arc weld
- arcback
- arch abutment
- arch brick
- arch core
- arch dam
- arch key
- arch lintel
- arch rise
- arch stress
- archaeology
- arched
- arched delta
- arched truss
- archimede pressure
- archipelago
- architectural acoustics
- architectural design
- architectural engineering
- archive
- archives
- arcuation
- area
- areal density
- areal erosion
- areaway
- arenaceous
- Argand lamp
- argil
- argilliferous
- argument field
- aridity index
- application characteristics
- application language
- application object
- application package
- application programming
- applications programmer
- applied informatics
- applied research
- appointment
- appraise
- appreciable error
- apprentice
- approach signal
- approver
- approximate to
- approximative method
- apyrous clay
- aqueduct
- aqueous
- aqueous rock
- aquifer
- arachnodactyly
- arbitrary distribution
- arbitrary sequence
- arbitrary unit
- arc arrester
- arc cutting
- arc resistance
- arc triangulation
- arc voltage
- arch
- arch chord
- arch cover