Quiz: Remember the definition of mal de mer?
Old English twelf, literally "two left" (over ten), from Proto-Germanic *twa-lif-, a compound of the root of two + *lif-, root of the verb leave (see eleven). Cf. 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."