The word 注射 is formed by combining two characters that each contribute a key action to the unified concept. The first character, 注 (zhù), carries the core meaning of "to pour" or "to concentrate (a fluid)". The second character, 射 (shè), means "to shoot", "to eject", or "to project". When combined, they sequentially depict the process of concentrating a liquid and then projecting it inward, creating a vivid conceptual image of the medical procedure of an injection, using a syringe to forcefully introduce a fluid into the body.