Why is the "Bb Bis" Key on Saxophones Named That Way?

Saxophones are not designed with a lot of alternate fingerings, but the note Bb is an exception - the Bb on the center line, and the Bb above the staff (same fingerings, plus the octave key) have 5 different possibilities. The most useful of these is the "bis" fingering, with the first finger of the left hand holding down both the B key and the little "bis" key directly below it.

I'd always wondered why the bis key had that name. I knew it meant "again" in French, but that didn't completely answer my question. This last summer I had the pleasure of meeting Xavier Sibre, a French sax/clarinet player who was visiting in Silicon Valley for a couple of weeks. He's back in Paris now. It occurred to me that Xavier might be able to give me a good answer to the "bis" etymology question, so I emailed him. Here's his answer:

Actually yes, "bis" means something in French. It means "double" as in the double of something already existing. For example, you would find a house on number 3 of a street and another house on 3 would be called 3bis. So concerning the Bb it means the bis key is like a second option towards the same result ;-) if you see what I mean. Just like a Bb number 2.

As nearly as I can tell, the first saxophones c. 1845 used a Bb fingering with the first two fingers of the LH, plus a RH side key, as on clarinet. According to Fred Hemke's 1975 dissertation "The Early History of the Saxophone," an 1886 patent application described a mechanism that allowed a Bb with LH first finger plus either first, second, or third finger of the RH (as on modern saxophones). In 1887, the bis key is described in a patent granted to Evette and Schaeffer, "allowing the Bb to be fingered with the first finger left hand alone."

In high school, my lessons were mostly on clarinet, from Paul Pone, who was an accomplished classical clarinetist, but not really a sax player, or a jazz guy. In college I signed on with Eddy Flenner, who was both a saxophonist and a jazz player. At my first lesson with Eddy, he asked me to play an F major scale for two octaves. I did, and Eddy asked me, "Why didn't you use the bis key?" I said, "What's that?" I had to spend some practice time learning to use it.

I teach students to use the bis Bb in most situations. Exceptions would be when going chromatically between B and Bb (usually the side fingering is better), and in a few rare situations (usually arpeggios when 1 and 1, 1 and 2, or 1 and 3 offers some advantage). If intonation needs to be adjusted, it's useful to remember that bis Bb is a little sharper than the other fingerings.

Here's a discussion of "bis" etymology from Sax on the Web - but I think Xavier's answer is about as clear as it could be.