Thank you all for your inputs!

The original Nix publication was helpful. On page 22 of the full thesis,
it says:
--8<---------------cut here---------------start------------->8---
Derivation is Nix-speak for a component build action, which derives
the component from its inputs.
--8<---------------cut here---------------end--------------->8---

Direct loan words similar to "derivasyon" are possible. But, they would
be a last resort. வழித்தோன்றல் is surprisingly good, but I think I'll
construct a calque along the lines of "build-message". That seems to be
the most meaningful approach.

It's probably too much trouble now, but even in English, it would help
to have something more descriptive than "derivation". I remember
struggling with the term when first introduced to Guix. "build-message"
would have been much more self-descriptive.

Cheers!