a mighty one: a man of outstanding strength and prowess, above all the warrior and the hero, and by extension God himself as the supreme champion.
At its heart this word names someone who is strong and able far beyond the ordinary, and proves it. It is not a description of muscle alone but of someone whose strength makes a difference: the soldier who wins battles, the famous champion whose name is remembered, the capable man of weight and standing in his community.
The word lives mostly on the battlefield. Its commonest use is the seasoned fighter, the man of war, and from there it becomes a near-title for an elite class of soldiers, most famously David's band of celebrated warriors. Reach a little wider and it can mark any man of conspicuous ability or standing, even where no fighting is in view, the man of valor, wealth, or proven competence.
Because the word reaches for the very top of human strength, it became a natural way to speak of God. When the Bible calls God a mighty one, it borrows the picture of the unbeatable warrior and turns it on the only one who is truly invincible. The same word that praises a human hero confesses that real, final might belongs to God, who fights for his people and cannot be overpowered.