Probably Arabic 'al-manakh' (the climate), but its exact origin remains one of English etymology's most stubborn puzzles.
An annual publication containing a calendar, astronomical data, tide tables, and other statistical information; originally a table of celestial movements.
From Medieval Latin 'almanach,' probably from Arabic 'al-manākh' (المناخ, 'the climate') or possibly from Arabic 'al-munākh' (the resting place of camels, hence a stopping point for the sun). The exact Arabic etymon is debated, but the word entered European languages through the astronomical tables produced by Arab and Moorish scholars in medieval Spain. Roger Bacon used the Latin form 'almanach' in 1267, referring to tables of planetary positions
The exact Arabic etymology of 'almanac' remains one of the great unsolved puzzles of English etymology — even the Oxford English Dictionary marks it as uncertain, with at least five competing Arabic source words proposed over the centuries.