Definition of aa in English:

aa

noun

Geology
  • Basaltic lava forming very rough jagged masses with a light frothy texture.

    Often contrasted with pahoehoe
    • ‘Roads of black ash traverse it, winding through the otherwise untraversable aa.’
    • ‘Very different from jagged aa, pahoehoe is the other general texture of newly solidified lava.’
    • ‘A serpentine flow meanders through formations of smooth pahoehoe lava and rough aa lava, the same forms common in basalt lavas.’

Origin

Mid 19th century: from Hawaiian ’ a-'a.

Definition of AA in English:

AA

  • 1Alcoholics Anonymous.

  • 2Antiaircraft.

  • 3Administrative assistant.

  • 4Associate of Arts.