The word 丝毫 is formed through the combination of two ancient, nearly synonymous measurement units to create an intensified abstract meaning of extreme minuteness. 丝 originally referred to the finest thread of silk, the smallest unit in traditional Chinese measurement, while 毫 referred to the tip of a fine hair or the tiniest unit of length and weight. By pairing these two characters, each representing the absolute extreme of smallness in the physical world, the compound solidifies and amplifies the conceptual idea of "the smallest possible amount" or "the slightest degree", moving from concrete measurements to a fixed idiom denoting negligible quantity.