The word 根深蒂固 is formed by combining two noun-adjective pairs: 根深, meaning "roots deep", and 蒂固, meaning "stem firm". These pairs are juxtaposed to create a four-character idiomatic compound where each pair describes a plant's foundational stability, and together they reinforce the literal image of deep roots and a solid base, leading to the figurative meaning of something deeply ingrained and firmly established.