The word **牢固 (láogù)** is formed through the compounding of two synonymous characters, each contributing to the overarching meaning of strength and stability. The first character, **牢 (láo)**, originally picturing an animal enclosure or pen, carries connotations of something secure, fast, and enduring. The second character, **固 (gù)**, means solid, hard, or firmly established. By combining them, the word creates a reinforced, idiomatic concept—much like "fast" and "secure" in English forming "fast-secure"—that vividly expresses a state of being firm, sturdy, and unyielding, whether applied to physical objects or abstract concepts like friendships or memories.