[sharpercoder]

One, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve... they're unique names. Then comes thirten, fourten.

Ten, eleven and twelve are unique names and probably have their entymology derived from a base-12 numbering system once primarily used in Anglo-speaking countries.

[Tistron]

It's simple enough to Google "etymology eleven" to see that it is a base 10 word.

Modern proponents of a dozenal system seem to prefer the words "el" and "doz" for eleven and twelve. I would totally be in for changing, but realistically it'll never happen.

Numberphile on the dozenal system: https://youtu.be/U6xJfP7-HCc

[occamrazor]

“Twelve” is suspiciously similar to “two” however, which makes me wonder about its origin.