from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
ESQUIRE. A title applied by courtesy to officers of almost every
description, to members of the bar, and others. No one is entitled to it by
law, and, therefore, it confers, no distinction in law.
2. In England, it is a title next above that of a gentleman, and below
a knight. Camden reckons up four kinds of esquires, particularly regarded by
the heralds: 1. The eldest sons of knights and their eldest sons, in
perpetual succession. 2. The eldest sons of the younger sons of peers, and
their eldest sons in like perpetual succession. 3. Esquires created by the
king's letters patent, or other investiture, and their eldest sons. 4.
Esquires by virtue of their office, as justices of the peace, and others who
bear any office of trust under the crown.