heads or tails

Attested since at least 1833, on the second page of Galignani's Messenger: "amusing themselves by pitching quoits, spoiling halfpence at heads or tails with the gingerbread merchants, drinking beer, smoking, etc".

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heads or tails

1. (idiomatic) The practice of flipping a coin in the air, to choose between two alternatives based on which side lands face up.

• make heads or tails of
• heads or harps
• toss a coin

• Coin flipping on Wikipedia.Wikipedia