An, AN, aN, or an may refer to:
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an in Wiktionary, the free dictionary.
- An, in mathematics, a root system and its Dynkin diagram
- An, in mathematics, conventional notation for the alternating group
- an, a generic label for a term of a sequence
- AN thread, Army and Navy thread - for bolts and tube fittings in 16th inch increments
- Acanthosis nigricans, a skin condition
- Acrylonitrile, an organic compound and monomer used in the manufacture of certain plastics
- Actinide (An), informal symbol for a series of chemical elements
- Ammonium nitrate (AN), a chemical compound
- Anode, in electronic schematics
- Anorexia nervosa, an eating disorder
- Application note (in engineering), most often seen as A.N.
- Attonewton (aN), an SI unit of force
- Anorthite, a feldspar mineral
- Adobe Animate, an Adobe animation software
- An (Shintō), a small table or platform used during Shinto ceremonies
- Anu or An, a god in Sumerian and Babylonian mythology