The word "activize" may not be a commonly used word in the English language, and therefore, it can be challenging to come up with antonyms for it. However, if we try to understand the meaning of activize, it can be inferred that it means to make something active or to activate it. Therefore, the antonyms for activize would be words that mean the opposite of activation or inactivity. Some possible antonyms for activize include deactivate, immobilize, pacify, calm, paralyze, still, and quiet. By using these antonyms, we can express the opposite of making something active and instead convey ideas of stillness and calmness.