The word "枯朽" is formed by combining two characters, each containing the radical "木" (wood) to semantically relate to plant material. The character "枯" incorporates "古" primarily for its phonetic contribution, meaning dry or withered, while "朽" incorporates "丂" for its phonetic role, meaning rotten or decayed. Together, they form a compound word emphasizing a state of deterioration, specifically decayed or withered.