A

Pronunciation (US):

• A (noun)
  The noun A has 7 senses:

1. a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation
2. any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes
3. one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose)
4. (biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA
5. the basic unit of electric current adopted under the Systeme International d'Unites
6. the 1st letter of the Roman alphabet
7. the blood group whose red cells carry the A antigen

  Familiarity information: A used as a noun is common.

• A (noun)

Meaning:

A metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation

Classified under:

Nouns denoting quantities and units of measure

Synonyms:

angstrom unit; angstrom; A

Hypernyms ("A" is a kind of...):

metric linear unit (a linear unit of distance in metric terms)

Meronyms (parts of "A"):

micromicron; picometer; picometre (a metric unit of length equal to one trillionth of a meter)

Holonyms ("A" is a part of...):

micromillimeter; micromillimetre; millimicron; nanometer; nanometre; nm (a metric unit of length equal to one billionth of a meter)

Meaning:

Any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes

Classified under:

Nouns denoting substances

Synonyms:

antiophthalmic factor; axerophthol; vitamin A; A

Hypernyms ("A" is a kind of...):

fat-soluble vitamin (any vitamin that is soluble in fats)

Hyponyms (each of the following is a kind of "A"):

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)

Meaning:

One of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose)

Classified under:

Nouns denoting substances

Synonyms:

deoxyadenosine monophosphate; A

Hypernyms ("A" is a kind of...):

nucleotide (a phosphoric ester of a nucleoside; the basic structural unit of nucleic acids (DNA or RNA))

Meaning:

(biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA

Classified under:

Nouns denoting substances

Synonyms:

adenine; A

Hypernyms ("A" is a kind of...):

purine (any of several bases that are derivatives of purine)

Domain category:

biochemistry (the organic chemistry of compounds and processes occuring in organisms; the effort to understand biology within the context of chemistry)

Holonyms ("A" is a substance of...):

deoxyribonucleic acid; desoxyribonucleic acid; DNA ((biochemistry) a long linear polymer found in the nucleus of a cell and formed from nucleotides and shaped like a double helix; associated with the transmission of genetic information)

ribonucleic acid; RNA ((biochemistry) a long linear polymer of nucleotides found in the nucleus but mainly in the cytoplasm of a cell where it is associated with microsomes; it transmits genetic information from DNA to the cytoplasm and controls certain chemical processes in the cell)

Meaning:

The basic unit of electric current adopted under the Systeme International d'Unites

Classified under:

Nouns denoting quantities and units of measure

Synonyms:

amp; ampere; A

Context example:

a typical household circuit carries 15 to 50 amps

Hypernyms ("A" is a kind of...):

current unit (a measure of the amount of electric charge flowing past a circuit point at a specific time)

Meronyms (parts of "A"):

mA; milliampere (one thousandth of an ampere)

Holonyms ("A" is a part of...):

abamp; abampere (a unit of current equal to 10 amperes)

Meaning:

The 1st letter of the Roman alphabet

Classified under:

Nouns denoting communicative processes and contents

Synonyms:

letter a; A

Hypernyms ("A" is a kind of...):

alphabetic character; letter; letter of the alphabet (the conventional characters of the alphabet used to represent speech)

Holonyms ("A" is a member of...):

Latin alphabet; Roman alphabet (the alphabet evolved by the ancient Romans which serves for writing most of the languages of western Europe)

Meaning:

The blood group whose red cells carry the A antigen

Classified under:

Nouns denoting body parts

Synonyms:

group A; type A; A

Hypernyms ("A" is a kind of...):

blood group; blood type (human blood cells (usually just the red blood cells) that have the same antigens)