definition of
A

[1] #1 A n. [angstrom, angstrom unit] a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation. wn

[2] #2 A n. [vitamin A, antiophthalmic factor, axerophthol] any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes. wn

[3] #3 A n. [deoxyadenosine monophosphate] one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose). wn

[4] #4 A n. [adenine] (biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA. wn

[5] #5 A n. [ampere, amp] the basic unit of electric current adopted under the Systeme International d'Unites; "a typical household circuit carries 15 to 50 amps". wn