Yours, Etc.: Origins and Uses of 8 Sign-Offs
late 14c., from Middle French esquier "squire," literally "shield-bearer" (for a knight), from Old French escuyer, from Vulgar Latin scutarius "shield-bearer, guardsman" (in classical Latin, "shield-maker"), from scutum "shield" (see hide (n.1)).
For initial e-, see especial. Cf. squire. Originally the feudal rank below knight, sense broadened 16c. to a general title of courtesy or respect for the educated class, especially, later, in U.S., for lawyers.
originally, a knight's shield bearer, who would probably himself in due course be dubbed a knight; the word is derived from the Old French esquier and earlier from the Latin scutarius.