Idk... I'm looking at the etymology for "dungeon"and it lists the German word "Tunk", meaning: “manure or soil covered basement, underground weaving workshop”. I kid you not. https://en.wiktionary.org/wiki/dungeon#Etymology
"Both the Frankish and Old English words derive from Proto-Germanic dungijǭ (“an enclosed space; a vault; bower; treasury”), from Proto-Indo-European dʰengʰ- (“to cover”), and are related to Old Saxon dung (“underground cellar”), Middle Dutch donc (“underground basement”), Old High German tung (“underground cellar; an underground chamber or apartment for overwintering”) (whence German Tunk (“manure or soil covered basement, underground weaving workshop”)), Old Norse dyngja (“a detached apartment, a lady's bower”) (whence Icelandic dyngja (“chamber”)). See also dung, dingle."
Well... According to Wiktionnary, it from the obsolete german word "dingen", of the same meaning. It seems to cognate somehow with the english word "thing" (and the german word "Ding").
German "dingen" and English "thing" are both from the Proto-Germanic word *þingą, which means an "assembly". Then it is a complicated story, you should look by yourself....
"Dongeon", however, cognate with the english word "dung". You probably can guess how.