The word "差不多" is formed through a conceptual fusion where the character "差", meaning "to lack" or "the difference", is directly modified by "不多", meaning "not much". This creates a literal, almost mathematical core idea of "the difference is not much" or "lacking by not much". Through common usage, this concrete notion evolved into a single, abstract adjectival and adverbial concept meaning "approximately", "almost", or "close enough", capturing the state where exact equivalence is not reached, but the shortfall is insignificant.