The word 刺激 is formed through semantic compounding, where two characters with related meanings combine to create a new, more nuanced concept. The first character, 刺 (cì), carries the core meaning of "to prick", "to stab", or "to irritate", evoking a sharp, penetrating action. The second, 激 (jī), means "to arouse", "to surge", or "to excite", suggesting a powerful, reactive wave of energy or feeling. Conceptually, they merge to depict the process where an external, often sharp or sudden, agent (刺) provokes an intense internal reaction or excitement (激), perfectly encapsulating the cause-and-effect nature of physical or psychological stimulation.