The phrase four-letter word is generally thought to originate in the late 1920s; various slang dictionaries have it from the late 20s or early 30s, and it achieved wider currency after 1934 when it was included in the lyrics of Cole Porter’s Anything Goes. The OED has four-letter man ‘an obnoxious person’ from 1923, but four-letter word not till 1934. So I was pleased – but also momentarily bemused – to find the following among a collection of witticisms entitled ‘By the Way’, from the Wall Street Journal of October 1, 1921:

This looks like a real and early instance of four-letter word being used to substitute for a vulgar word; it’s not yet generic (in the sense that four-letter words would soon come to mean profanity, in general) but it’s the earliest case I can find of the phrase being used at all as a form of taboo avoidance. Also, unlike later uses, which tend, I think, to take fuck or shit as the prototypical four-letter word, here I think it’s a substitute for hell. Get hell ‘to be severely punished’ has now faded from use (I might say catch hell instead, although even that feels old-fashioned) , but in the early to mid-20th century, both ‘raise hell’ and ‘get hell’ were relatively common idiomatic phrases:
In other (four-letter) words, Russia has been raising hell, and Lenin (Lenine was a 1920s variant) would like America to get hell. The WSJ did not have a prohibition against hell appearing at its pages at this point, although it certainly wasn’t common. Or maybe there is some other obvious four-letter word (vulgar or otherwise) that collocates with raise and get and would be witty in this context. Your thoughts?