Interchangeable means capable of being interchanged, substituted or replaced by something else without affecting the overall function or quality. Antonyms of interchangeable are fixed, permanent and unchanging. Fixed means securely in place and unlikely to move or change, while permanent means lasting or intended to last indefinitely without change. Unchanging means staying the same in all circumstances, and not susceptible to alteration or modification. Synonyms for interchangeable, on the other hand, include exchangeable, switchable and replaceable which describe something that can be easily swapped out or substituted with another option.