The word 免疫 is formed by combining two characters: 免 (miǎn), which carries the core meaning of "to avoid", "to be exempt from", or "to avert", and 疫 (yì), which specifically means "epidemic" or "pestilence". Conceptually, they fuse to create the idea of "exempting oneself from an epidemic" or "averting disease", which directly corresponds to the biological concept of immunity. It is a semantic compound where the combined meaning emerges logically from the individual parts.