On the origins of "Esquire" (or "Esq.") as an honorific for lawyers:
The word itself derives from Old French, and in turn from Latin, where it means something like “shield-holder.” In the 1200s and 1300s in England, a variety of languages were used, so such figures might be referred to as the … French escuier, which became “esquire.” These terms all refer to roughly similar people. This role was generally considered moderately prestigious for young men of some wealth, but at its core it was a service job. You carry a knight’s stuff, tend to his horses, that kind of thing. “Esquire” and “squire” were names for the same gig for a few hundred years.