Almagest

Origin

Arabic المجسطي (al-majisṭī, "almagest"), which is an addition of the Arabic definite article to a transliteration of Ancient Greek μεγίστη ("greatest")

Full definition of almagest

Noun

1. A comprehensive treaty on astronomy, geography, and mathematics compiled by Ptolemy circa 150 CE.
2. Any of several medieval treatises, especially those concerned with astronomy or alchemy.