also AA, abbreviation of Alcoholics Anonymous, attested by 1941, American English. The group name was the title of a book published in 1938 by the founder, Bill W. From 1914 as an abbreviation of anti-aircraft guns.
a la carte
a la mode
a posteriori
a priori
A&P
A.A.
A.A.A.
A.B.
A.D.
A.H.
a.k.a.