almanac (n.) Look up almanac at Dictionary.com
late 14c., attested in Anglo-Latin from mid-13c., via Old French almanach or Medieval Latin almanachus, of uncertain origin. It is sometimes said to be from a Spanish-Arabic al-manakh "calendar, almanac," but possibly ultimately from Late Greek almenichiakon "calendar," which is said to be of Coptic origin.

This word has been the subject of much speculation. Originally a book of permanent tables of astronomical data; one-year versions, combined with ecclesiastical calendars, date from 16c.; "astrological and weather predictions appear in 16-17th c.; the 'useful statistics' are a modern feature" [OED].