Is "idiomático" a false friend of "idiomatic"?

Question

At English Language & Usage SE there are sometimes questions about usage that get an answer something like this:

You could say that, and people would understand you, but it's not idiomatic. That is, it doesn't sound natural to a native speaker of English.

Can I use idiomático in a similar way in Spanish?

I was assuming yes, but a comment has made me doubtful now.

For reference, the DLE definition of idiomático says:

1. adj. Propio y peculiar de una lengua determinada.

2. adj. Ling. Dicho generalmente de una expresión lingüística: Que posee un significado no deducible del de los elementos que la componen.

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What I'm trying to find out is whether, as the comment asserted, I should not assume I can use the two words in a similar way. And if the answer is, "No, Aparente, be careful with that word, it doesn't match up the way one might think just by looking at it," then I'd like to understand how they are different.

In other words, can I say something like

Podrías decirlo, y se te entendería, pero la frase así como la propones no es idiomática. Es decir, no se oye natural para un hispanoparlante nativo.

(See top of question for context.)

Or is that a misuse of the word idiomático?

In short: ¿Es idiomática la palabra "idiomático"?

Answer 1

I think idiomático could be easily mistaken or simply not understood in Spanish. If you said to me about an expression «Eso no es idiomático», I would have to ask for clarification, since I wouldn't understand if you meant "That is not grammatically correct" or "That is not how you say it".

It would be a bit different if you said, in the affirmative, «Ésa es una expresión idiomática», because that would ring a bell and it would correspond to one of the DLE's definitions: it's either a peculiar way of saying a thing or a fixed phrase (an idiom). In the negative, again, it would be confusing: does «Ésa no es una expresión idiomática» mean "That is not a correct expression" or "That is not a proper expression"?

"Sounding natural to speakers of a given language" and "being peculiar/specific to a given language" are in a sense complementary and can be seen as equivalent. If you feel the need to specify that a certain expression "sounds natural to speakers of language X", it's probably because it doesn't sound natural to you, who speak another language, because it's "peculiar to language X". Otherwise you wouldn't mention it at all.

Answer 2

They are not false cognates, since both derive from the Ancient Greek ἰδιωματικός (idiōmatikós, “related to an idiom”), but they can be false friends (See here for more info):

False friends are words in two languages that look or sound similar, but differ significantly in meaning.

Note, they do coincide in the secondary definition:

Resembling or characteristic of an idiom. // Dicho generalmente de una expresión lingüística: Que posee un significado no deducible del de los elementos que la componen.

so for this, they are neither false cognates nor false friends.