In checking out a site tsuwm provided a while back, I came across this passage:

"The sequence continues with quaternary, quinary, senary, septenary, octonary, nonary, denary. Words also exist for `twelfth order' (duodenary) and `twentieth order' (vigenary)."

When would you use words, such as nonary, and if duodenary is twelfth order, what would eleventh order be?

But, more to the point, in what kinds of applications would you use these higher orders? I'm familiar with using primary and secondary sources....but I doubt anyone would refer to duodenary sources!