It's not a new word. People have been using the word "transpiler" or "transcompiler" for source-to-source compilers since at least the late 80's [0]. They used to be popular for translating between different dialects of assembly. Then they fell out of fashion for a while before gaining popularity again in the last decade for targeting JavaScript. So while the "JS world" is responsible for re-popularizing both the word and the concept, they certainly didn't invent it.

[0]edit: Apparently 60's.