late 14c., from Middle French esquier "squire," literally "shield-bearer" (for a knight), from Old French escuier "shield-bearer (attendant young man in training to be a knight), groom" (Modern French écuyer), from Medieval Latin scutarius "shield-bearer, guardsman" (in classical Latin, "shield-maker"), from scutum "shield" (see escutcheon). For initial e-, see e-. Compare squire (n.). Originally the feudal rank below knight, sense broadened 16c. to a general title of courtesy or respect for the educated and professional class, especially, later, in U.S., regarded as belonging especially to lawyers.
In our own dear title-bearing, democratic land, the title of esquire, officially and by courtesy, has come to include pretty much everybody. Of course everybody in office is an esquire, and all who have been in office enjoy and glory in the title. And what with a standing army of legislators, an elective and ever-changing magistracy, and almost a whole population of militia officers, present and past, all named as esquires in their commissions, the title is nearly universal. [N.Y. "Commercial Advertiser" newspaper, quoted in Bartlett, 1859]