So I was reading Kikko's rather amusing Liarville, a political reworking of an old rakugo story, when I came across a word I don't remember encountering before: peten, ペテン.

It's clear in context that it means a fraud or a con game, and there's an associated word petenshi (ペテン師) that means "con man" or "swindler". But where does peten come from and why is it in katakana?

None of my sources dare call it certain, but most cite the same likely source: a Chinese word bengzi also meaning "fraud" (繃子), borrowed into Japanese as pentsu (c.f. mianzi 面子 → mentsu, "face"). This then got flipped to peten -- not impossible; it happened to arata → atara[shii], after all.

(As for why 繃子, which my dictionary defines as a hoop for embroidery, should mean "fraud", I do not know. Maybe it's just a homophone using the same hanzi because no-one ever bothered to assign different ones.)

My single rebel source is MAEDA Isamu's Edogo no jiten, which explains petenshi as follows:

In yashi [mountebank, snake-oil salesman] slang, a peten referred to a head, hat or umbrella. Possibly an inversion of tenpe(n) [天辺, older pronunciation of modern teppen meaning "top"]

... which is a much more colorful explanation, except that Maeda doesn't provide any examples of this usage, nor an account of why "head" would come to mean "fraud" anyway. And he also includes the 繃子 explanation, so he can't be that sure. Bah!