The word "牢牢" is formed through the morphological process of reduplication, specifically the AA-pattern, where the base adjective "牢" (láo), meaning "firm", "secure", or "fast", is duplicated. This repetition serves to intensify and emphasize the core meaning, transforming it from simply "firm" to "firmly", "securely", "tightly", or "unshakably". It functions as an adverb and conveys a strong, often enduring sense of stability, fixation, or unwavering certainty, as in "牢牢记住" (remember firmly) or "牢牢抓住" (hold on tightly).