# A (disambiguation)

(Redirected from A (song))

A is the first letter of the Latin alphabet.

A may also refer to:

## Science

• 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
• Alanine, amino acid
• 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.

### Mathematics and logic

• A numerical digit meaning ten in hexadecimal and other positional numeral systems with a radix of 11 or greater
• Sometimes in blackboard bold represents the algebraic numbers (${\displaystyle \mathbb {A} }$) (U+1D538 in Unicode)
• Universal quantifier in symbolic logic (symbol ∀ or ${\displaystyle \forall }$, an inverted letter A)
• Universal affirmative, one of the four types of categorical proposition in logic
• Mills' constant is represented by the symbol A
• Glaisher–Kinkelin constant is also often represented by the symbol A

## Linguistics

• 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