The phrase "lets out" can be interpreted in different ways. When we say "lets out," it can mean releasing something, disclosing information, or emitting a sound or noise. In the context of releasing something, antonyms for "lets out" can include withhold, keep in, retain or hold. When talking about revealing information, antonyms for "lets out" could be keep secret, conceal, hide or cloak. Finally, when referring to sound or noise, the antonyms for "lets out" can be quieten, silence, or hush. It is essential to understand the context to identify the appropriate antonym to use.