The word 防止 is formed through semantic combination, where two independent characters, each with their own meaning, are joined to create a new, unified concept. The first character 防 (fáng) carries the core idea of "defending against" or "guarding", while the second character 止 (zhǐ) means "to stop" or "to halt". Their combination is not merely additive but synthesizes into the proactive concept of "to prevent", essentially, to take guarding measures (防) in order to stop something (止) from occurring. This formation is a classic example of a complementary compound in Chinese, where the second character specifies the result or purpose of the action denoted by the first.