You can think of a short stick, heavy at the far end, held in one hand. No edge, no point, no aim to speak of. Everything it does comes from weight arriving somewhere. That is the picture the whole word seems to grow out of: one meaning is the stick itself, one is bringing it down on someone, and the rest move the same blunt weight into words and into the way a person pushes forward.
From the word’s history
Wiktionary records bludgeon as first attested in 1730, with an uncertain origin: perhaps Cornish (written blogon around 1450), or from Middle French bougeon, a small form of bouge meaning club or stick. Both suggestions point at the same thing — a stick — which is the image the modern senses still work from.
Wiktionary 記載 bludgeon 最早出現在 1730 年，來源並不確定：一說可能來自康瓦爾語（1450 年前後寫作 blogon），一說來自中古法語 bougeon，也就是 bouge（棍子）的小稱。兩種說法指向同一樣東西——一根棍子——而那正是今天所有用法還在用的畫面。
Wiktionary, "bludgeon"
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