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Citation Information
How to Cite
Hendrickson, Robert. "aa." Writer's Reference Center. Facts On File, Inc. Web. 17 Apr. 2025. <http://fofweb.infobase.com/wrc/Detail.aspx?iPin=EWPO00002>.
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aa

Definition 
Aa for rough porous lava, similar to coal clinkers, is an Americanism used chiefly in Hawaii, but it has currency on the mainland, too, especially among geologists, or where there has been recent volcanic activity, mainly because there is no comparable English term to describe the jagged rocks. The word aa is first recorded in 1859, but is much older, coming from the Hawaiian 'a'a, meaning the same, which, in turn comes from the Hawaiian a, for "fiery, burning."

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