The compound adjective 'well-grounded' is built from native English elements. The core concept stems from the Old English noun grund, meaning the solid bottom of something, which evolved into the verb 'to ground' in the sense of establishing a firm foundation. The adverb 'well,' signifying thoroughness or correctness, intensifies this foundational quality. Thus, the literal sense of "thoroughly based" evolved from the physical idea of being built on solid ground to the modern abstract meanings of being logically sound or thoroughly trained in fundamentals.

Structure: well (thoroughly) + ground (base) + ed (adjective suffix) - well: From Old English wel, meaning "in a good way, thoroughly." It functions as an intensifying adverb modifying the participle. - ground: From Old English grund, meaning "bottom, foundation, base." Here, it is the past participle of the verb 'to ground,' meaning to provide a basis or foundation. - ed: A suffix from Old English -od/-ad, used to form adjectives from verbs or nouns, indicating a state or condition.