Knave

Knave [noun]: a dishonest or unscrupulous man; a scoundrel; someone worthless because they lie or steal. It was formerly used to mean merely a boy or servant.

It could be said that McEachern referred to Joe as a knave because McEachern assumes whatever Joe has done [and is doing] beyond his presence or knowledge is inherently sinful.

In LIA, McEachern had punished Joe for coming home later than curfew and afterwards, studied Joe's face and decided he'd been in a fight; McEachern demanded to know with whom and what for. Joe would not disclose the reason but did admit that he had fought more than one opponent. McEachern spoke, "you mean you cant tell or you wont tell? Then, if you dont know you are a fool. And if you wont tell you have been a knave. Have you been to a woman?" "No." "You have never lied to me. That I know of, that is. Who were you fighting with?" "There was more than one." [160]