Arborvitae

Arboviral encephalitides

Arboviral encephalitis

Arc discharge

Arc flash hazard

Arc heating

Arc lamp

Arc welding

Arcellinida

Arch

Arch bridge

Archaea

Archaeocyatha

Archaeognatha

Archaeopteridales

Archaeopteryx

Archaic ungulate

Archean

Archeoastronomy

Archeological chemistry

Archeological chronology

Archeology

Archiacanthocephala

Archidiidae

Archigregarinida

Archimedes' principle

Architectural acoustics

Architectural engineering

Archosauria

Arctic and subarctic islands

Arctic Circle

Arctic engineering

Arctic marine transportation

Arctic mining technology

Arctic Ocean

Arctic Ocean freshwater balance

Arctic Oscillation

Arctic sea-ice monitoring

Arcturus

Area

Arecales

Arecidae

Arenaceous rocks

Argentiniformes

Argillaceous rock

Argo (ocean observing network)

Argon

Arhynchobdellida

Aries

Aristolochiales

Arithmetic

Arkose

Armadillo

Armature

Armature reaction

Army armament

Aromatic hydrocarbon

Aromatization

Arrow of time

Arsenic

Art conservation chemistry

Artemisinin

Arteriosclerosis

Artesian system

Arthritis

Arthropod evolution and phylogeny

Arthropoda

Artichoke

Articulata (Echinodermata)

Artificial intelligence

Artificial photosynthesis

Artificial spinal disc replacement

Artificial sweetener

Artificially layered structures

Artiodactyla

Asbestos

Asbestos measurement

Ascaridida

ASCE program for sustainable infrastructure

Ascidiacea

Ascothoracica

Ash

Asia

Asian vegetable

Asparagales

Asparagus

Aspartame

Aspect-oriented software development

Asphalt and asphaltite

Aspidogastrea

Aspidorhynchiformes

Aspirin

Assembly machines

Assessing risks from nanomaterials

Assisted GPS and location-based services

Assisted migration for species preservation

Assisted reproductive technology

Astatine

Asterales

Asteridae