prig, n.² — Green’s Dictionary of Slang

prig n.²

[? it is ‘pricked’ with spurs]

a horse.

prig-napper (n.) [nap v.¹ (2)]

(UK Und.) a horse-thief.

1674		Head Canting Academy (2nd edn) n.p.: prig-napper A Horse-stealer.
c.1698		B.E. Dict. Canting Crew n.p.: Prig-napper A Horse-stealer.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].