Definition of aa in English:

aa

noun

Geology
  • [mass noun] 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.’
    • ‘A serpentine flow meanders through formations of smooth pahoehoe lava and rough aa lava, the same forms common in basalt lavas.’
    • ‘Very different from jagged aa, pahoehoe is the other general texture of newly solidified lava.’

Origin

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

Pronunciation:

aa

/ˈɑːɑː/

Definition of AA in English:

AA

  • 1Alcoholics Anonymous.

  • 2Anti-aircraft.

  • 3(in the UK and South Africa) Automobile Association.

Pronunciation:

AA

/eɪˈeɪ/