Basaltic lava forming very rough, jagged masses with a light frothy texture.
'Roads of black ash traverse it, winding through the otherwise untraversable aa.'
Alcoholics Anonymous.
Anti-aircraft.
(in the UK and South Africa) Automobile Association.
noun
1.
basaltic lava having a rough surface.
Examples:
"There can be aa lavas." "There can be aa wirs." "There can be aa weapons." "There can be aa strumpets." "There can be aa groups." "There can be aa dustbins." "There can be aa changes." "There can be aa chairmen."
