The word "不朽" (bù xiǔ) is formed through the logical combination of two characters: the negation adverb "不," meaning "not" or "un-," and the verb "朽," which means "to decay," "to rot," or "to become worm-eaten." When combined, the literal meaning is "does not decay," which is then extended metaphorically to signify something that is enduring, imperishable, or immortal, most commonly used to describe everlasting fame, legacy, or spirit. This formation follows a standard grammatical structure in Chinese where an adverb modifies a verb to create a new, often abstract, compound word.