1. A comprehensive treatise on astronomy, geography, and mathematics compiled by Ptolemy about A.D. 150.
2. almagest Any of several medieval treatises concerned with astronomy or alchemy.

[Middle English almageste, from Old French, from Arabic al-majisti : al-, the + Greek megistē (suntaxis), greatest (composition), feminine of megistos, greatest.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.