From Proto-Italic *tondeō, from Proto-Indo-European *tend- (“to split, cut off”).
See also Latin temnō, tempus, templum, Ancient Greek τέμνω (témnō), Welsh tam (“morsel”), Middle Irish tamnaim (“I cut off”), Proto-Slavic *tęti "to split, cleave", and the second element of Latin aestimō (“to appraise, value, estimate”).