The list of banned words for US radio and television is in a U.S. Supreme Court report — called FCC v Pacifica Foundation (438 US 726, 57 L Ed 2d 1073, 98 S Ct 3026). The case was about a radio program called "Filthy Words", sp[oken over the air on 20 October 1973, by a "satiric humorist named George Carlin" (I quote from the report at 438 US 729). The court report includes a transcript of the radio program.

The original seven words were shit, piss, fuck, cunt, cocksucker, motherfucker, and tits.

Three more words you could never say on television were fart, turd, and twat. Fart is harmless. It's like tits. Cutie word, no problem. Turd you can't say, but who wants to? But "twat" is interesting ... Twat!

Twat is interesting because it's the only word know applying to a part of the sexual anatomy that doesn't have another meaning. Snatch, box, and pussy all have other meanings. Even in a Walt Disney movie, you can say, 'We're gonna snatch that pussy, and put him in a box and put bring him on the airplane.' But twat stands alone.

(Incidentally, the UUS Supreme Court, by a majority, said that the Federal Communications Commission could stop radio stations broadcasting stuff like that, at times when children were likely to be listening, in spite of the First Amendment to the US Constitution.)

What about euphemistic or 'hidden' references to 'forbidden' words, such as the increasingly popular "X-word" form?

Forms such as "the f-word" (fuck), and so on, have now branched out into politically correct usage, i.e. to cover words not considered politically-correct in context. Other examples include "the D-word" ("dynamic", used as code for "male" in university teacher ads), or "the L-word" ("ladylike", as a counterpart in the same article).