twelve (adj., n.)
"1 more than eleven, twice six; the number which is one more than eleven; a symbol representing this number;" Old English twelf "twelve," literally "two left" (over ten), from Proto-Germanic *twa-lif-, a compound of *twa- (from PIE root *dwo- "two") + *lif- (from PIE root *leikw- "to leave"). Compare eleven. Cognate with Old Saxon twelif, Old Norse tolf, Old Frisian twelef, Middle Dutch twalef, Dutch twaalf, Old High German zwelif, German zwölf, Gothic twalif. Outside Germanic, an analogous formation is Lithuanian dvylika, with second element -lika "left over."