Not in any dictionary I could find, but here is definition in a quote:
"The single horseman had mended his pace, when he first observed
the three riders advance rapidly towards him; but when he saw
them halt and form a front, which completely occupied the path,
he checked his horse, and advanced with great deliberation; so
that each party had an opportunity to take a full survey of the
other. The solitary stranger was mounted upon an able horse, fit
for military service, and for the great weight which he had to
carry, and his rider occupied his demipique, or war-saddle, with
an air that showed it was his familiar seat. "