Doug Miller wrote:

But that's *not* what lye is. Lye is sodium hydroxide.

It can be either.

Not correct. Lye is specifically NaOH.

The lye made from ashes is potash lye, potassium
hydroxide.

OK, fine, but "lye" and "potash lye" are not the same thing.

Potassium hydroxide came first, as a result of the very natural and
ancient process of rain falling on forest fires. It is the stuff for
which the word "lye" was coined centuries ago.

http://m-w.com/dictionary/lye

Sodium hydroxide is a manmade and much more recent compound. The oldest
process for its manufacture seems to date to 1772.

http://en.wikipedia.org/wiki/Sodium_hydroxide

So I maintain that KOH is the original lye, and NaOH has glommed onto
the name simply by becoming the more common and cheaper caustic.