Green’s Dictionary of Slang

1. a highwayman.

1599

Nashe Praise of the Red Herring 53: He fell into the thieuish hands of malcontents and launceknights.

2. a horse-thief who owns his own horse.

1591		Greene Second Part of Conny-Catching in Grosart (1881–3) X 76: The Priggar if he be a Launce man, that is, one that is already horst, then he hath more followers with him, and they ride like Gentlemen.
1608		Dekker Belman of London G2: The Prigger, who trauailes vp and downe the whole kingdom vpon his gelding [...] [is] called a Prigging lance-man.