Where does “castelli” come from?

castelli (Welsh) comes from Welsh i, from Middle Welsh y, from Old Welsh ir, from Proto-Celtic sindos, from Proto-Indo-European sḗm, from Proto-Indo-European sem- — together, one.

Ancestry of “castelli”, step by step

castelli traces back through two separate lines of ancestry.

via Welsh i

StepLanguageWordMeaning
1WelshiI, me; to, for; that
2Middle Welshyhis, its with reference to a masculine noun; triggers soft mutation of following consonant
3Old Welshirthe
4Proto-Celticsindosthis
5Proto-Indo-Europeansḗmone
6Proto-Indo-Europeansem-together, one

via Welsh castell

StepLanguageWordMeaning
1Welshcastellcastle; rook
2Latincastellumcastle, fort, citadel, fortress, stronghold; a...
3Latincastrumcastle, fort, fortress; camp, especially a...
4Proto-Italickastromknife
5Proto-Indo-Europeanḱos-tróm
6Proto-Indo-Europeanḱes-to cut off, separate; to cut up, to slaughter; to...
Every word from Proto-Indo-European sem-Every word from Proto-Indo-European sḗmEvery word from Proto-Celtic sindos