From Latin coctorium (“casserole, pan”), probably from coctor (“cook”), from coquō. Compare also Albanian koftor, Italian cottoio, Catalan cuitor.
cuptor n (plural cuptoare)
2) (popular) July (seventh month of the Gregorian calendar)
From Wiktionary: https://en.wiktionary.org/wiki/cuptor
I know that others might perceive your comments as spam, but actually I find them quite handy. I was just thinking of equivalents in other Romance languages (horno,forno) and missed the connection. Good that you clear it up and good that Duolingo has a comment section.