The word "故意" is formed through a conceptual fusion of its two component characters. "故" carries meanings related to something old, a former state, a cause, or, critically here, an act done with prior knowledge or deliberation. "意" means intention, thought, or meaning. When combined, the concept is not merely additive but synthetic: the "deliberate" or "knowing" aspect of "故" merges with the "intent" of "意" to create a single, cohesive idea of an action performed with conscious purpose or premeditation, hence meaning "on purpose" or "intentionally".