Encyclopedias, Almanacs, Transcripts, and Maps
- Abū Yūsuf
- Abulafia, Meʾir
- Academy Award
- Academy awards (‘Oscars’) — best film
- Acanthocephala (Thorny Headed Worms)
- Acanthuroidei (Surgeonfishes and Relatives)
- accents
- Accounting for Nature
- Acehnese Religion
- Acid and Base
- Acid Deposition
- Acid Mine Drainage
- Acidification
- Acipenseriformes (Sturgeons and Paddlefishes)
- Acoela (Acoels)
- Acosta, Gabriel
- act of Congress
- act of Parliament
- Activated Sludge
- Actors Studio