One of the problems is that you might not use the target language at the equivalent level of abstraction. For example, C is a popular target language, but the C emitted may be very unidiomatic and nothing like human consumable code, it's not all that unusual that a language compiles all code to one big C function where the function calls in the language are jumps, which is a way to get around the limitations of the C calling conventions and stack.

The same thing applies to compilation to Javascript, the resulting code may use a tiny subset of the language.

I don't like the word transpiler, because there is nothing useful about the distinction (unless you count people using it to denigrate compilers that doesn't target traditional machine code).

I could see the case of using it as a name when the transformation is reversible, like you could probably turn Javascript back into Coffeescript.

What value does the word have? When I'm writing a compiler, it doesn't matter whether I target C or asm, or Javascript, as my output language. I'll still write it the same way.

OK, but words are not only for compiler-writers. As someone who encounters your compiler, if it targets an output language at a similar level as the input language it will give me a headstart in understanding what it does if I see it referred to as a transpiler rather than simply a compiler.

Overall, I find this discussion very odd. It seems like a kind of deletionism for the dictionary. I mean, what's the use of the word 'crimson'? Anything that's crimson is also just 'red'. Why keep 'large' when we have 'big'? You could delete a large percentage of English words by following this line of thinking.

It gives you a better idea what a thing does?

To me, it doesn't. If someone says "tsc is a transpiler", it gives me nothing actionable. If you do say "it transpiles to JS", then I've got something, but that could just be "compiles to JS". It doesn't really tell me how the thing is constructed either.