The word 注入 is formed by combining two individual characters, each contributing its core meaning to create a new, composite concept. The first character, 注 (zhù), originally depicts the idea of pouring water, carrying connotations of concentrating or directing a flow. The second character, 入 (rù), is a pictograph meaning "to enter" or "to go into". When joined, they create a vivid conceptual metaphor: to "pour-into". This visually suggests the action of introducing one substance or entity into another, such as injecting a liquid, infusing capital, or channeling energy into a system, forming a single verb that encapsulates the entire process of internal introduction.