How many letters does the top answer for “a manner of speaking that is natural to native speakers of a language” have?

The most common answer is idiom (5 letters).

Crossword clue: a manner of speaking that is natural to native speakers of a language

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

idiom 5 letters wn-def

a manner of speaking that is natural to native speakers of a language

parlance 8 letters wn-def

a manner of speaking that is natural to native speakers of a language