- A, type A, group A - the blood group whose red cells carry the A antigen
--1 is a kind of blood group, blood type
- angstrom, angstrom unit, A - 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 is a kind of metric linear unit
--2 is a part of
--2 has parts: picometer, picometre, micromicronnanometer, nanometre, nm, millimicron, micromillimeter, micromillimetre - vitamin A, antiophthalmic factor, axerophthol, A - any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes
--3 is a kind of fat-soluble vitamin
--3 has particulars: vitamin A1, retinol; vitamin A2, dehydroretinol - deoxyadenosine monophosphate, A - one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose)
--4 is a kind of nucleotide
- adenine, A - (biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA
--5 is a kind of purine
--5 is a substance ofdeoxyribonucleic acid, desoxyribonucleic acid, DNA; ribonucleic acid, RNA - ampere, amp, A - the basic unit of electric current adopted under the Systeme International d'Unites; "a typical household circuit carries 15 to 50 amps"
--6 is a kind of current unit
--6 is a part of abampere, abamp
--6 has parts: milliampere, mA - A - the 1st letter of the Roman alphabet
--7 is a kind of letter, letter of the alphabet, alphabetic character
--7 is a member of Roman alphabet, Latin alphabet