Think about it. You’ve got the base numbers, one through ten. Almost every number after that, from 12 on, makes obvious sense language-wise because they start with the same letters (two, twelve, twenty; three, thirteen, thirty; four, fourteen, forty, and so on).

And then there’s eleven. “Eleven” is nothing like “one.” So where did it come from?

Some digging revealed that the word is of Old English origin. It came from endleofan, which meant 11, or more literally “one left over.” In fact, twelve is formed in a similar way; it evolved from “two left over” into the Old English twelf. From there on, in the rest of the sequence, teen stands for “ten.”

This begs one question: Why the different references for 11 and 12 than for the teen numbers? It’s very likely due to the fact that England employed a base-12 systems for many common measurements (a 12-hour clock, 12 inches in a foot, 12 pence to a shilling, 12 ounces in a Troy pound, and so on). The numbers 11 and 12 cropped up more often than larger numbers did, so it made sense to refer to them as “left over” from 10.