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c.1200, elleovene, from Old English endleofan, literally "one left" (over ten), from Proto-Germanic *ainlif- (cf. Old Saxon elleban, Old Frisian andlova, Dutch elf, Old High German einlif, German elf, Old Norse ellifu, Gothic ainlif), a compound of *ain "one" (see one) + PIE *leikw- "leave, remain" (cf. Greek leipein "to leave behind;" see relinquish).
FIREFLY: Give me a number from 1 to 10.Viking survivors who escaped an Anglo-Saxon victory were daroþa laf "the leavings of spears," while hamora laf "the leavings of hammers" was an Old English kenning for "swords" (both from "The Battle of Brunanburgh"). Twelve reflects the same formation. Outside Germanic the only instance of this formation is in Lithuanian, which uses -lika "left over" and continues the series to 19 (vienio-lika "eleven," dvy-lika "twelve," try-lika "thirteen," keturio-lika "fourteen," etc.) Phrase eleventh hour (1829) is from Matthew xx:1-16.