Slavic [[dupa]]

Thank you for finally giving reasons for one of your reverts, o CodeCat!

Still, your revert goes against the etymology of dupa/dziupla/dno (q.v.) as given in Słownik etymologiczny języka polskiego, Wiesław Boryś, Kraków 2005, see here for this very entry or in the truncated Słownik Języka Polskiego here. In short, e.g. dno <- *dъbno -< *dhub-no- od *dheṷ-b- (/*dheṷ-p-). Ditto in (agreed, very dated) Bruckner, who is providing the cognate Lithuanian [[dauba], dubus, and dubti, while for the latter originating from *dheṷ-b-, see Bronius Piesarskas and Bronius Svecevicius: Lithuanian Dictionary and Webster's Seventh New Collegiate Dictionary (1963).

Do your sources claim otherwise? If so, please provide their ety. If not, please revert yourself and fix further. Chwała!