The word "shiftable" refers to something that can be moved or changed. Its antonyms would include words that indicate the opposite, such as immovable, fixed, stationary, rigid, or inflexible. An object that is considered shiftable is one that can be adjusted or adapted to different circumstances, but its opposite, immovable, suggests something that cannot be changed or altered. Fixed or unchanging are also antonyms to shiftable, indicating the opposite of flexibility. In summary, antonyms for shiftable would be words that suggest inactivity and a lack of adaptability or adjustability.