Heh.
I can tell you that Gary Gygax explained it to a table of GenCon gamers, in my hearing, as "THACK-oh." And that's the only way I ever heard old guard designers at TSR pronounce it. I, too, have heard other pronunciations since.— Ed Greenwood (@TheEdVerse) July 14, 2021
How do you pronounce THAC0?
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