A
A is often used as a shorthand for American, especially in demographic or national contexts. In specialized fields it can denote the Anglo‑American Cataloguing Rule, an animal classification, an allergist, or an analog signal.
Medical
Albino guinea pig
Arterial
Area
antinuclear antibody (ANA is more commonly used)
anoxia/reoxygenation
Anion
Animal
Anaphylaxis
Amphetamine
alveolar gas
Allergist
Allele
Arteriolar
Alanine
Akinetic
Adults & Communities
Adriamycin
Adrenaline
admittance Electricity
Acetum
Actin
Actinomyces
Adenosine
Asbestos
Ant
Anteater
Ankle Jerk/Reflex
auris (ear)
apical/radial
mass number
Adenine
Axis
Auricular
augmenting reducing
Animals
Atropine
Atrium
Atrial
Alveolization
Asparagine
Miscellaneous
Annealing
Ages
Accusative
A-check
Alex
Asexual
Awesome
Ann
Acre
Aperture
Apron
Appropriate
Ape
Apple
Arte
Community
Governmental
International
Academic & Science
Advanced
Atomic
Adjective
Anode
Absorptivity
Australian
Atom
Art
Against
The Arts
Anglo American Cataloguing Rule
Aakash