红眼
hóngyǎn · HSK 7
Red eye
👁️ 红 (red) + 眼 (eye) = red eye; also slang for envious, like being red-eyed with jealousy
红 means red and 眼 means eye, so 红眼 is literally red eye. The same compound doubles as a word for envy or jealousy (think red-eyed with envy), and names the overnight red-eye flight.
红 — silk radical 糹/纟 + work 工 (phonetic)
红 is a semantic-phonetic compound. The silk radical 糹 (simplified 纟) signals the meaning, since the character originally referred to a kind of pink or light-red dyed silk. The right side 工 supplies the sound. Over time the meaning broadened from the dye color to 'red' in general.
眼 — eye radical 目 + 艮 (phonetic)
眼 is a semantic-phonetic compound. The left side 目 means 'eye' and gives the meaning, while 艮 on the right supplies the sound. Originally referring to the eyeball, it broadened over time to mean 'eye' generally and, by extension, 'a hole' or 'key point'.