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 communications 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?

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 communications 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?