The word 替代 is formed by combining two characters with closely related meanings to reinforce a single core concept. The first character, 替, originally depicted two people standing side by side (one replacing the other), conveying the idea of "to substitute" or "to replace". The second character, 代, carries the meaning of "to act on behalf of" or "to take the place of". When paired, they create a compound where both components contribute the notion of one thing standing in for another, resulting in the comprehensive meaning of "to substitute" or "to take the place of".