The antonyms for the word "most loosened" are "tightened," "fixed," and "secure." When something is tightened, it means that it is made more secure and less likely to move or become loose. Fixing something involves making it stable and strong, leaving no room for any looseness. Something that is secure is firmly in place and cannot move or be easily removed. The opposite of most loosened is something that is stable, strong, or secure. These antonyms are particularly relevant when describing the state of objects, furniture, or other physical things.