Aa – definition of aa by The Free Dictionary

AA abbr. 1. Bible Acts of the Apostles 2. Alcoholics Anonymous 3. antiaircraft 4. Associate in Arts a·a or a’a (ä′ä) n. Lava having a rough surface. [Hawaiian ‘a’ā, to burn, aa.] aa (ˈɑːɑː) n (Geological Science) a volcanic rock consisting of angular blocks of lava with a very rough surface [Hawaiian] aa abbreviation for ana1 AA abbreviation …

: https://www.thefreedictionary.com/aa