The word 地道 is formed through a conceptual metaphor where the character 地 (earth/ground) and 道 (path/way) are combined. It first literally means an underground tunnel, a man-made "way/passage" through the "earth". This tangible, hidden, and functional passageway metaphorically evolves to describe something (like flavor, skill, or accent) that is genuine, authentic, and true to its local origins, as if it emerges directly from and is deeply rooted in the very "earth" or soil of a specific place, following the true "path" or essence of that locality.