In French, the word for ‘impossible’ is ‘impossible’.
This word is pronounced quite similarly to English, as it retains the same spelling and meaning. However, the pronunciation has a distinctly French accent, which might take some practice if you’re just starting to learn the language. In conversations, you would use it in context similar to how you would in English, such as saying, ‘C’est impossible’, which translates to ‘It’s impossible’.