The word 案子 is formed through a common Chinese morphological process where the core meaningful character 案 (àn), which originally means "table" or "legal case", is combined with the suffix 子 (zi). This suffix 子, when used in this way, often serves to nominalize or concretize a concept, transforming the base meaning into a more tangible or specific noun. In this instance, it takes the abstract idea of a "case" or "matter" from 案 and turns it into the more concrete and commonly used term for a "lawsuit" or "legal case". The formation is purely about building a specific, stand-alone word from a meaningful root and a functional, meaning-modifying unit.