cfront compiled C++ to C, so it's a transpiler, right? Or is that just an unimportant implementation detail?
Everything targeting LLVM IR is a transpiler, because it's just source-to-source, with the second source being LLVM IR.
Similarly things targeting the JVM or CLR - all transpilers because both of these are relatively high level targets. They might not be something you would consider a "source language", but for many people assembly language is a perfectly reasonable source language, and thus...
Everything compiling to assembly language is a transpiler. The target language is assembly.
Having worked on compilers for over two decades it just comes across as a made-up term by people who don't understand that what a compiler does is translate from one language to another (be it another "source language", ASTs, linear IRs, VM bytecodes, assembly languages, or executable code).
I don't think I'm being particularly pedantic here. Compilers simply generate another form that one person or another might consider a source language (in fact people working on JITs most definitely think of their input as the source language).