> I've always thought, albeit vaguely, that Z for the integers came earlier
> than Bourbaki from German Zyklus or zyklisch, as in cyclic group.
I think that in fact it comes from "Zahlen", the German word for
(integral) number.
> I can't
> think of a comparable origin for Q, unless maybe from Latin quantum or a
> related Latin word, as in "quantity" or "how much", perhaps meant to refer
> to the fact that measurements made by physicists, chemists, engineers,
> carpenters, etc., generally turn out to be rational numbers.
I always thought it was from the German for fraction, which is
something like "Querschnitt". I believe the letters Q,R,C for
rationals, reals, complexes, had some currency before Bourbaki
made them universal, but am not sure where I got this from; I
wonder what letters Landau used in his little book?
John Conway