almagest (n.) Look up almagest at Dictionary.com
late 14c., title of a treatise on astronomy by Claudius Ptolemy of Alexandria, extended in Middle English to other works on astrology or astronomy, from Old French almageste (13c.), from Arabic al majisti, from al "the" + Greek megiste "the greatest (composition)," from fem. of megistos, superlative of megas "great" (see mickle). Originally titled in Greek Megale syntaxis tes astronomios "Great Work on Astronomy;" Arab translators in their admiration altered this.