The adjective debonair (which can mean "suave" or "nonchalant") was first used in the Ancrene Riwle, a mid-thirteenth century monastic manual, when it was spelled deboneire. Other forms after that have included de bonere, debonayre, deboner, debonaire, debonnair, debonnaire, and many others. The word comes from the Old French de bon' aire, which literally meant "of good race". Pure lineages were associated with high class, so that's how the "suave" definition came about, and then that developed a more carefree connotation later on. De, through Latin, traces to a Proto-Indo-European root sounding the same and also meaning "of". Bon' is an abbreviation of bone, from Latin bonus (also "good"), and ultimately derives from Proto-Indo-European dew, "to show favor". Finally, aire has an uncertain origin but could be from ager, the Latin word for "field".
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.