Fluent means speaking a language smoothly and easily. Fluent in French, fluent English, speak fluently.
It describes flow rather than perfection: a fluent speaker keeps going without hunting for words, and may still make mistakes. That is why fluent and accurate are separate things and why teaching aims at both. Fluent in is the usual construction. Note fluency; and that the word comes from the Latin for flowing, which also gives fluid, influence and affluent.
1adjectivefluentSpeaking a language smoothly and easily.
“After living in Paris for years, she's now fluent in French.”
fluent is a quality of smooth speech.
Latin fluens is the present participle of fluere, to flow. Fluid, influence, affluent and superfluous come from the same flowing.
Latin
fluens — flowing
English, today
fluent
Built from
From Latin fluens (“flowing”), present active participle of fluō (“to flow”).
Etymology from Wiktionary, CC BY-SA