Contrails are the visible trails of condensed water vapor made by aircraft. An antonym is a word that means the opposite of another word. When it comes to antonyms for contrail, we can consider the absence of trails left in the sky by aircraft. Some antonyms for the word contrail are the clear sky, unclouded, bright, and sunny. These words describe the opposite of the visible trails left behind by planes in the sky. While contrails can sometimes be a beautiful sight to see, the absence of them can also be equally as stunning on a clear, bright day.