Language has incredibly subtle nuances that mean different words change meaning in various ways, and the ways in which they change it vary between speaker and listener. Unless the speakers of a language decide that the nuances aren't worth the effort of maintaining more than one word for the same thing, in which cases, less favoured words die out. You used the word "isotonic" instead of "equivalent" or "synonymous", presumably for good reason.

In my mind, "code" implies something opaque, mysterious, and difficult, rather than something which is open to all.

But "coder" is a good signal that they don't know what they're talking about, the term is only used by journalists and politicians.

that's not true, its very popular outside of web development in general day to day use as slang.

in my circle we probably use it much more than 'developer', which is a woolly term that encompasses all kinds of artists, designers, producers, teams and whole companies. although the standard term is definitely 'programmer'.

I have always seen 'coder' used for someone who essentially transforms designers intent into HTML/CSS/JS (or other GUI code) and does not especially care about backend code. I have seen it used with this meaning even in job postings (mostly web development related).

i dont have much contact with that part of the programming world (although i work in a web dev office atm) - every time i've heard it used its to refer to a programmer working on performance critical desktop software or AAA games... that's the opposite end of the spectrum pretty much.