感染
かんせん · kansen · JLPT N1 · noun
infection
🦠 感 (sense) + 染 (dye, stain): germs dye you from outside, which is infection
染 means to dye or stain, and 感 relates to influence or feeling. A pathogen stains the body from outside, so 感染 means infection or contagion, the spread of germs between people.
感 — heart 心 + 咸 (xián, phonetic)
A semantic-phonetic compound. The heart radical 心 at the bottom carries the meaning of feeling or emotion, while 咸 supplies the sound. Together 感 conveys being moved in the heart, hence 'to feel,' 'sense,' or 'be affected by' something.
染 — water 氵 + nine 九 + wood 木
染 depicts the dyeing process: 氵 (water) for the dye liquid, 木 (wood) for plant-based dyestuffs, and 九 (nine) suggesting repeated dippings to deepen the color. Originally meaning 'to dye cloth,' it later extended to figurative senses like 'to be influenced' or 'to contract' (as in illness).