A

(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.

(noun) any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes. Synonyms: vitamin A, antiophthalmic factor, axerophthol.

(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.

(noun) (biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA. Synonyms: adenine.

(noun) the basic unit of electric current adopted under the Systeme International d'Unites. Synonyms: ampere, amp. Examples: "A typical household circuit carries 15 to 50 amps."

(noun) the 1st letter of the Roman alphabet. Synonyms: a.

(noun) the blood group whose red cells carry the A antigen. Synonyms: type A, group A.