"Transpiler" is short for "transcompiler". Has been since the 80's.
And what verb do you use with a transpiler? It compiles one form into another.
A transpiler is a source-to-source compiler. What you do with the output afterwards hardly matters, when it is performing the act of compilation.
There is no distinction here. One is merely a subset of the other. Which is good for communicating purpose, but you can't just assume one is seperate from the other when they employ the same process.
A compiler may not compile to a source language, though it might.
A transpiler is a compiler that compiles to a source language.
> Citation needed that either of these terms actually existed before 2013.
Your own sources have references in '03, which contradicts that.
But I'll oblige.
Sitting on my shelf is
"XLT86 - 8080 to 8086 Assembly Language Translator, User Guide", dated 1982. (But not the version you can find online, which is September, '81. I'm not quite sure on the release, as the user guides didn't include a revision number).
Here's a quote:
> XLT86·is a Digital Research software product that aids in the translation of 8080 assembly language programs to equivalent 8086 programs.
...
> Unlike other 8086 trans-compilers, XLT86...
> The XLT86 trans-compiler is available for operation under CP/M and MP/M for the 8080, 8085, and Z80...
So, I would say Digital Research coined the term in '81, but their usage suggests that others in that circle would occasionally use the term, or have a passing familiarity with such a term.
Likewise, there are compilers I wouldn't call transpilers.