A (disambiguation)

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A is the first letter of the Latin alphabet.

A may also refer to:


  • A battery, a vacuum tube filament battery
  • Vitamin A, also called retinol, an essential human nutrient
  • Haplogroup A (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup
  • Haplogroup A (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup
  • A+ and A-, human blood types
  • Adenine, nucleic acid
  • Alanine, amino acid
  • Adenosine, nucleoside
  • ATC code A, Alimentary tract and metabolism, a section of the Anatomical Therapeutic Chemical Classification System
  • Anode, an electrode
  • The center of a hexagonal face of the Brillouin zone of a hexagonal lattice, in physics
  • The letter "A" was formerly the chemical symbol for the element argon, which is now indicated by the symbol Ar.


Abbreviations for physical and chemical quantities and units[edit]

Mathematics and logic[edit]


The arts[edit]




Film ratings[edit]




  • A and an, the indefinite article in English
  • A, the agent-like argument of canonical transitive verb
  • A (or a), the first letter of the Latin alphabet
  • A (Cyrillic) (A or а), the first letter of the Cyrillic alphabet
  • Alpha (Α or α), the first letter of the Greek alphabet
  • A (kana) (or a), the romanized name of the Hiragana syllable letter あ and of the Katakana syllable letter ア used in Japanese, which may also be used to represent Asia
  • a, the IPA representation of the open front unrounded vowel
  • ɑ, the IPA representation of the open back unrounded vowel
  • a., an abbreviation of ante (Latin for "before") used in etymologies




See also[edit]