A

Definitions of A
  1. noun
    the 1st letter of the Roman alphabet
    synonyms: a
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    type of:
    alphabetic character, letter, letter of the alphabet
    the conventional characters of the alphabet used to represent speech
  2. noun
    any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes
    synonyms: antiophthalmic factor, axerophthol, vitamin A
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    types:
    retinol, vitamin A1
    an unsaturated alcohol that occurs in marine fish-liver oils and is synthesized biologically from carotene
    dehydroretinol, vitamin A2
    a viscous alcohol that is less active in mammals than is vitamin A1
    type of:
    fat-soluble vitamin
    any vitamin that is soluble in fats
  3. noun
    the blood group whose red cells carry the A antigen
    synonyms: group A, type A
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    type of:
    blood group, blood type
    human blood cells (usually just the red blood cells) that have the same antigens
  4. noun
    the basic unit of electric current adopted under the Systeme International d'Unites
    synonyms: amp, ampere
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    type of:
    current unit
    a measure of the amount of electric charge flowing past a circuit point at a specific time
  5. noun
    a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation
    synonyms: angstrom, angstrom unit
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    type of:
    metric linear unit
    a linear unit of distance in metric terms
  6. noun
    one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose)
    synonyms: deoxyadenosine monophosphate
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    type of:
    base, nucleotide
    a phosphoric ester of a nucleoside; the basic structural unit of nucleic acids (DNA or RNA)
  7. noun
    (biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA
    synonyms: adenine
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    type of:
    purine
    any of several bases that are derivatives of purine
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