à marquer d'une pierre blanche

== French == === Etymology === Literally, “to mark with a white stone”. === Pronunciation === IPA(key): /maʁ.ke d‿yn pjɛʁ blɑ̃ʃ/ === Verb === marquer d'une pierre blanche (transitive, figuratively) to remember as a red letter day, to mark as a milestone, to see as a landmark event un jour à marquer d'une pierre blanche ― a day to remember as a red letter day