Sprachgefühl
Etymology
German, from "Sprache" (language, speech) and "Gefühl" (feeling) — literally "language-feeling." Borrowed into English in the nineteenth century as a term of art among philologists and linguists.
noun · /SHPRAHKH-guh-fyool/
An intuitive, almost instinctive feel for what is natural or correct in a language.
What it names
The unteachable ear that tells you a sentence is off before you can say which rule it broke — the sense fluent speakers trust over grammar books.
Example
No rule forbade the phrasing, but her Sprachgefühl flinched at it — a native speaker would never say it that way.
Related idea
Where syntax is the explicit, statable system of rules, Sprachgefühl is the tacit intuition that operates beneath them.