The phrase "letted out" means to release or allow something to escape or exit. Some of the antonyms for this phrase can include confine, restrain, hold in, trap, or keep inside. For example, if someone is let out of prison, the antonym would be to confine them. Similarly, if a pet is let out of its cage, the antonym would be to keep it restrained. In many cases, the opposite of letting something out involves keeping it confined or under control. By understanding the antonyms for "letted out," we can better express the opposite meanings of this phrase in different contexts.