The compound word **腐朽** is formed through the combination of two semantically related characters, **腐** (fǔ), meaning "rotten" or "decayed" (as in decomposing matter), and **朽** (xiǔ), meaning "rotten" or "decayed through age" (as in brittle, crumbling wood). Each character reinforces the other, creating a powerful parallel structure where their individual meanings of physical decay and degradation merge to form a single, amplified concept. This union results in a term that literally describes something rotten and crumbling, but is more commonly used metaphorically to depict ideas, systems, or morals that are corrupt, degenerate, and hopelessly out-of-date.