The word "根本" is formed by combining two characters, "根" meaning "root" (as in the root of a plant) and "本" meaning "base", "origin", or "foundation". Both characters individually convey ideas related to the bottom or source of something, and when joined, they reinforce each other to create a compound that emphasizes the fundamental, essential, or core aspect of a matter, metaphorically extending from the physical concept of roots and base to abstract notions of essence and necessity.