So post the question here:
I'm stumped. Anyone has any idea why we say 'heads or tails?' rather than 'head or tail?' when flipping a coin?
Medieval in origin. Monks would engrave their favorite slogans on the front and back of coin units to be used as talismans, which gave rise to expressions such as, heads or tails and six of one half-dozen of the other, which fell into disuse sometime after the invention of the two-headed coin, subsequent to which, you had to flip sides of the same.Originally Posted by NewHope