Synonyms/Hypernyms (Ordered by Estimated Frequency) of noun a

7 senses of a

Sense 1
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)
       => metric linear unit -- (a linear unit of distance in metric terms)

Sense 2
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)
       => fat-soluble vitamin -- (any vitamin that is soluble in fats)

Sense 3
deoxyadenosine monophosphate, A -- (one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose))
       => nucleotide, base -- (a phosphoric ester of a nucleoside; the basic structural unit of nucleic acids (DNA or RNA))

Sense 4
adenine, A -- ((biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA)
       => purine -- (any of several bases that are derivatives of purine)

Sense 5
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")
       => current unit -- (a measure of the amount of electric charge flowing past a circuit point at a specific time)

Sense 6
A, a -- (the 1st letter of the Roman alphabet)
       => letter, letter of the alphabet, alphabetic character -- (the conventional characters of the alphabet used to represent speech; "his grandmother taught him his letters")

Sense 7
A, type A, group A -- (the blood group whose red cells carry the A antigen)
       => blood group, blood type -- (human blood cells (usually just the red blood cells) that have the same antigens)