The word "不可或缺" is formed by sequentially combining the characters "不" (not), "可" (can), "或" (or), and "缺" (lack), creating a literal meaning of "cannot or lack". The construction functions as a fixed phrase where "不可" serves as a negation of capability, and "或缺" presents the condition of absence, together conveying that something is not permissible to be missing or is absolutely necessary.