A (noun)
1: the blood group whose red cells carry the A antigen [syn: A, type A, group A]
2: a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation [syn: angstrom, angstrom unit, A]
3: any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes [syn: vitamin A, [[antiophthalmic factor]], axerophthol, A]
4: one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose) [syn: deoxyadenosine monophosphate, A]
5: (biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA [syn: adenine, A]
6: the basic unit of electric current adopted under the Systeme International d'Unites; "a typical household circuit carries 15 to 50 amps" [syn: ampere, amp, A]
7: the 1st letter of the Roman alphabet [syn: A]