My understanding (from a talk by Rob Bradley) is that Cauchy is responsible for
the now-standard $\epsilon{-}\delta$ formulation of calculus, introduced in his
1821 _Cours d’analyse_.  Although perhaps instead it was introduced by Bolzano a few years
earlier.  My question is not about who was first with this notation, but 
rather:

> Why were the symbols $\epsilon$ and $\delta$ used?

Why not, say, $\alpha$ and $\beta$?
(Imagine how different our mathematical discourse would be...)
Are there appropriate (French) words beginning with '_e_' and/or '_d_' that determined the choice?
Or perhaps Cauchy used up $\alpha,\beta,\gamma$ for other purposes prior to introducing $\delta,\epsilon$?  Does anyone know?