The word "most paperthin" can be described as something that is extremely thin and delicate, almost like tissue paper. Antonyms of this phrase could include words that describe thickness, durability, and strength such as sturdy, thick, robust, and substantial. These words signify solidity and strength, which are the opposite of the paper-thin quality. Other antonyms could be words like substantial, dense, or heavy, which adds the idea of weight and substance to the object or material. These antonyms help to create a more nuanced understanding of the word "most paperthin" as they help to identify and describe objects that are thicker, sturdier, and more durable.