"Knock-out" is a term used to describe something that is impressive or striking. There are many synonyms that can be used in place of "knock-out," such as breathtaking, spectacular, stunning, extraordinary, remarkable, amazing, and outstanding. These words can be used to describe anything from a performance, a piece of artwork, a vacation destination, or even a person's appearance. They all convey a sense of awe and admiration, and emphasize the idea that whatever is being described is truly exceptional. Using these synonyms instead of "knock-out" can add depth and richness to your language, making your writing or speech more engaging and memorable.