Definition of


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

via WordNet, Princeton University

Origin of the word A

  1. indefinite article, c.1150, a variation of O.E. an (see an) in which the -n- began to disappear before consonants, a process mostly complete by mid-14c. The -n- also was retained before words beginning with a sounded -h- until c.1600; it still is retained by many writers before unaccented syllables in h- or (e)u-, but is now no longer n… more
  2. as in twice a day, etc., from O.E. an "on," in this case "on each." The sense was extended from time to measure, price, place, etc. The habit of tacking a onto a gerund (as in a-hunting we will go) died out 18c. more

via Online Etymology Dictionary, ©2001 Douglas Harper

Words that sound like A

a.e., aa, aaa, aah, ai, aiai, au, away, awe, ayah, aye-aye

via soundex() Hash Matches

Note: If you're looking to improve your vocabulary right now, we highly recommend Ultimate Vocabulary Software.

Word of the Moment


a stony meteorite consisting of silicate minerals