The word "讳莫如深" is formed from four characters: 讳 (huì, meaning to conceal or avoid mentioning), 莫 (mò, meaning not or no one), 如 (rú, meaning like or as), and 深 (shēn, meaning deep). These characters combine in sequence to create a literal sense of "conceal so that no one knows as if it were deep", originating from a historical context in the "Zuo Zhuan" where a secret was tightly guarded. The phrase functions as an idiomatic expression where each character contributes to the overall meaning of closely keeping something secret or being highly reticent about a matter.