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ultima ratio regum

[oo l-ti-mah rah-tee-oh rey-goo m; English uhl-tuh-muh rey-shee-oh ree-guh m]
Latin.
  1. the final argument of kings (a resort to arms): motto engraved on the cannon of Louis XIV.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018