The word protractile means capable of being extended or stretched out. Its antonyms, on the other hand, are words that mean the opposite. They include words such as fixed, immovable, inflexible, rigid, stiff, and unyielding. These words describe objects or entities that cannot be stretched or extended in any way. Antonyms of protractile are often used in biology, engineering, and physics, where they describe structural properties of cells, materials, or machines. Using such words can help to convey a clearer meaning in writing and improve communication and understanding between people.