"possessed of or endowed with might; having much ability, strength, or power," Old English mihtig, earlier mæhtig, from Proto-Germanic *mahtiga- (source also of Old Frisian mechtig, Old Saxon mahtig, Dutch machtig, German mächtig), from the source of might (n.). As an adverb, "very, exceedingly, greatly," it is attested from c. 1300, though such use now is considered colloquial.
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, "The Creole Village," in The Knickerbocker, or New-York Monthly Magazine, November 1836]
Related: Almightily; almightiness. A 15c. text translates omnipotencia with allmyghtyhede "almightihood."
fem. proper name, from Irish Brighid, goddess associated with fire, spring, fertility, healing, poetry and smithcraft, from brigh "strength," from Celtic *brig-o-, from PIE *bhrgh-nt- "high, mighty," from root *bhergh- (2) "high."