Sentence:  But, before the defendant takes the oath, the plaintiff is called by the crier thrice; and if he do not appear he becomes nonsuited, and then the defendant goes quit without taking his oath; and if he appear, and the defendant swear that he owes the plaintiff nothing, and the compurgators give it upon oath, that they believe he swears true, the plaintiff is barred for ever; for when a person has waged his <WSD>law</WSD>, it is as much as if a verdict had passed against the plaintiff; if the plaintiff do not appear to hear the defendant perform his <WSD>law</WSD>, so that he is nonsuit, he is not barred, but may bring a new action. 
Meaning of the word marked with <WSD> tags:  An oath sworn before a court, especially disclaiming a debt. (wager of law)", "(wage one's law)", "(perform one's law)", "(lose one's law)".