[esrauch]

I think you are confused by terminology here and not by behavior, "immutable variable" is a normal terminology in all languages and could be says to be distinct from constants.

In Rust if you define with "let x = 1;" it's an immutable variable, and same with Kotlin "val x = 1;"

[psychoslave]

Lore and custom made "immutable variable" some kind of frequent idiomatic parlance, but it’s still an oxymoron in their general accepted isolated meanings.

Neither "let" nor "val[ue]" implies constancy or vacillation in themselves without further context.

[esrauch]

Words only have the meaning we give them, and "variable" already has this meaning from mathematics in the sense of x+1=2, x is a variable.

Euler used this terminology, it's not new fangled corruption or anything. I'm not sure it makes too much sense to argue they new languages should use a different terminology than this based on a colloquial/nontechnical interpretation of the word.

[psychoslave]

I get your point on how the words meanings evolves.

Also it’s fine that anyone name things as it comes to their mind — as long as the other side get what is meant at least, I guess.

On the other it doesn’t hurt much anyone to call an oxymoron thus, or exchange in vacuous manner about terminology or its evolution.

On the specific example you give, I’m not an expert, but it seems dubious to me. In x+1=2, terms like x are called unknowns. Prove me wrong, but I would rather bet that Euler used unknown (quantitas incognita) unless he was specifically discussing variable quantities (quantitas variabilis) to describe, well, quantities that change. Probably he used also French and German equivalents, but if Euler spoke any English that’s not reflected in his publications.

[SetTheorist]

"Damit wird insbesondere zu der interessanten Aufgabe, eine quadratische Gleichung beliebig vieler Variabeln mit algebraischen Zahlencoeffizienten in solchen ganzen oder gebrochenen Zahlen zu lösen, die in dem durch die Coefficienten bestimmten algebraischen Rationalitätsbereiche gelegen sind." - Hilbert, 1900

The use of "variable" to denote an "unknown" is a very old practice that predates computers and programming languages.

[psychoslave]

Yes sure, I didn't mean otherwise, but I just wanted to express doubts about Euler already doing so. Hilbert is already one century forward.