late 14c., "book of permanent tables of astronomical data," attested in Anglo-Latin from mid-13c., via Old French almanach or directly from Medieval Latin almanachus, a word of uncertain origin and the subject of much speculation. The Latin word is often said to be ultimately from Arabic somehow, but an exact phonological and semantic fit is wanting: OED connects it to a supposed Spanish-Arabic al-manakh "calendar, almanac," which is possibly ultimately from Late Greek almenichiakon "calendar," which itself is said to be of Coptic origin. But the author of English words of Arabic Ancestry makes a detailed case "that the word almanac was pseudo-Arabic and was generated within the circle of astronomers in Paris in the mid 13th century."
One-year versions, showing correspondence of days of the week and month, ecclesiastical calendars, etc., date from 16c.; "astrological and weather predictions appear in 16-17th c.; the 'useful statistics' are a modern feature" [OED].