twelveyoudaoicibaDictYouDict[twelve 词源字典]
twelve: [OE] Etymologically, twelve probably means ‘two over’ (just as eleven means ‘one over’). It appears to go back to a prehistoric Germanic compound formed from *twa- ‘two’ and *lif- (a relative of English leave), which also produced German zwölf, Dutch twaalf, Swedish tolf, and Danish tolv. If so, its underlying meaning is ‘two left (over ten)’, hence ‘ten plus two’.
=> leave, two[twelve etymology, twelve origin, 英语词源]
twelve (adj.)youdaoicibaDictYouDict
Old English twelf "twelve," 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). Compare 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."