Yeah, I found "crust" to be rather counter-intuitive. I think one of the reasons that bugs me is that "ret" and "mut" don't have any intrinsic meaning in English, but my brain insists on reading "crust" as if it were a word.

I'd personally have gone with "rustc".

"rustc" is how you invoke the compiler from the command line, that's no good. :)

I do seem to remember that the devs were passively soliciting ideas for a better name for this keyword. The great thing about a language at this stage is that if this really bothers you, then you can petition to have it changed!

How about externc, hinting at C++'s extern "C" for C++ code that will be visible (unmangled) to C code?

I actually like that a lot - relatively short, to the point, and doesn't have any conflicting intrinsic meaning.