\ ˈä-ˌä How to pronounce aa (audio) , ä-ˈä \
variants: or a'a

Definition of aa

 (Entry 1 of 4)

: basaltic lava having a rough, broken surface This jumble of two-year-old black rock is of the type known as aa (pronounced ah-ah). This is the term borrowed from the Hawaiian language for lava that is broken, jagged and angular, in contrast to the smooth or rope-textured pahoehoe …— Kendrick Frazier Aa is formed from stiffer, more viscous lava with a thick brittle crust that becomes broken and heaped up as it is carried along by the molten lava beneath.Science News The same eruption of lava can switch from pahoehoe to a'a, depending on factors such as thickness and how fast it's cooling.— Gemma Tarlach — compare pahoehoe

Definition of aa (Entry 2 of 4)

\ ˈdə-bəl-ˈā How to pronounce AA (audio) \
plural AAs

Definition of AA (Entry 3 of 4)

Definition of AA (Entry 4 of 4)

1 administrative assistant
2 Alcoholics Anonymous
3 antiaircraft
4 arachidonic acid
5 associate in arts
6 author's alterations

First Known Use of aa

Noun (1)

1859, in the meaning defined above

Noun (2)

1937, in the meaning defined above

History and Etymology for aa

Noun (1)

borrowed from Hawaiian 'a'ā "to burn, lava with a broken surface, abounding in such lava"

Keep scrolling for more

Learn More about aa

Statistics for aa

Cite this Entry

“Aa.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/aa. Accessed 4 Dec. 2020.

Keep scrolling for more

More Definitions for aa

variants: also aa

Medical Definition of āā

 (Entry 1 of 2)

of each used at the end of a list of two or more substances in a prescription to indicate that equal quantities of each are to be taken

Medical Definition of AA (Entry 2 of 2)

2 Alcoholics Anonymous

History and Etymology for aa


Latin ana

More from Merriam-Webster on aa

Britannica.com: Encyclopedia article about aa

Comments on aa

What made you want to look up aa? Please tell us where you read or heard it (including the quote, if possible).


Test Your Vocabulary

Musical Words Quiz

  • gramophone
  • Which word describes a musical performance marked by the absence of instrumental accompaniment?
Spell It

Can you spell these 10 commonly misspelled words?

Syn City

Test Your Knowledge - and learn some interesting things along the way.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!