Aa

Pronunciation

• RP IPA: /ˈɑː.ɑː/, enPR: ä'ä
• US IPA: /ˈɑ.ɑː/
• Rhymes: -ɑː

Alternative forms

• a'a

Origin

From Hawaiian ʻaʻā.

Noun

1. (volcanology) A form of lava flow associated with Hawaiian-type volcanoes, consisting of basaltic rock, usually dark-colored with a jagged and loose, clinkery surface. Compare pahoehoe. First attested in the mid 19^th century.
• 1859, R. C. Haskell, American journal of science and arts, series XXVIIIWe...saw ‘pahoihoi’ or solid lava forming, and also ‘aa’ or clinkers.
• 1883, Clarence E. Dutton, Fourth Annual report of the United States Geological Survey:The second form of the lavas is called by the natives a-a, and its contrast with pahoehoe is about the greatest imaginable. It consists mainly of clinkers sometimes detached, sometimes partially agglutinated together with a bristling array of sharp, jagged, angular fragments.
• 1944, Charles A. Cotton, Volcanoes as landscape forms:Cooling and solidification frequently takes a different course ... in lava flows, producing the clinker-like ‘aa’ lava.
• 1999, A. Ganeri: Violent Volcanoes:A'a is thick, sticky lava which forms jagged, chunky rock when it cools.
• 2004, Richard Fortey, The Earth, Folio Society 2011, p. 44:I overheard a geologist say that a good pair of boots can be rasped to bits on a‘a in a couple of months.
2. Initialism of acetic acid
3. Initialism of acting age
4. Abbreviation of adjectives
5. (medical) Initialism of alveolar-arterial
6. Initialism of aminoacetone
7. Initialism of approximate absolute
8. Initialism of arachidonic acid
9. Initialism of armature accelerator
10. Abbreviation of arteries
11. Initialism of ascending aorta
12. Initialism of atomic absorption
13. Initialism of author's alteration
14. Initialism of average audience

Full definition of aa

Adjective

1. Initialism of arctic-alpine

Initialism

1. Always afloat
2. Ana

Abbreviation

1. Equal parts