What does the root mis as in missile means?

The root "mis-" in "missile" does not mean anything. It is a mistake to think of it as a separate root.

The word "missile" comes from the Latin word "missilis," meaning "to throw or send." This word was adapted into English, and its meaning remains the same.

The word "missile" does not contain the root "mis-," which typically means "wrong, bad, or ill."