felon > [you are a felon, you are a villain] read > observe; realize; declare
3 How that you are partaker of his crime:
How > [In] partaker of > [a] participant in
4 Therefore, by Termagant, you shall be dead!"
Termagant > {Conflated with Mohammed as a Saracen god, or reckoned to be his partner, by the Crusaders: the name may derive from the Persian tir-magian, meaning a magian lord or deity; or from "Tervagan", a proper name in Chanson de Roland. See OF 12.59}
5 With that his hand, more sad then lump of lead,
sad > heavy, heavily
6 Uplifting high, he weened with Morddure,
Uplifting > Raising weened > thought, intended, meant
7 His own good sword Morddure, to cleave his head.