Old English ælmihtig "all-powerful," also a by-name of God; compound of æl (see all) + mihtig (see mighty); common Germanic (cognates: Old Saxon alomahtig, Old High German alamahtic, German allmächtig, Old Norse almattigr), perhaps an early Germanic loan-translation of Latin omnipotens (see omnipotent). Originally only of deities; general use is by late 14c.
The almighty dollar, that great object of universal devotion throughout our land. [Washington Irving, 1836]
Related: Almightily; almightiness. A 15c. text translates omnipotencia with allmyghtyhede "almightihood."