Stewart,
The names refer to the DESIGN of the lenses...you can see the history on
. 'Sonnar' is based on sonne, German for sun, for ex&le.
I had thought that maybe CZ had trademarked more generic names, at least for 'Planar' (a Planar/Planer design is a flat field design), but apparently it was Carl Zeiss who invented the Planar design, so they get to name it.
Biogon and Sonnar are also CZ inventions, but they were a bit vague about Distagon, which is a retrofocus WA design. No doubt their name, but maybe not their design.
It seems -ar is for relatively longer focal lengths, while -on is for wide angles.
BTW, I did also happen to see that it was CZ lenses used by Andrew Lesnie to shoot the Lord of the Rings films...