Where does “тупенький” come from?

тупенький (Russian) comes from Russian тупо́й, from Old East Slavic тупъ, from Proto-Slavic tǫpъ — dull, blunt.

Ancestry of “тупенький”, step by step

StepLanguageWordMeaning
1Russianтупо́йdull, blunt
2Old East Slavicтупъ—
3Proto-Slavictǫpъdull, blunt
Every word from Proto-Slavic tǫpъ →Every word from Old East Slavic тупъ →Every word from Russian тупо́й →