混雑
こんざつ · konzatsu · JLPT N3 · noun
congestion
🚃🚗 混雑 = mix (混) + assorted (雑): everything jumbled together, a crowd
混 means to mix, as in 混ぜる (mazeru, to stir). 雑 means assorted or rough, as in 雑誌 (zasshi, a magazine full of mixed articles). Mix lots of assorted people into one place and you get 混雑, a crowded jam.
混 — water radical 氵 + 昆 (kūn, phonetic)
A semantic-phonetic compound: 氵 (water) gives the meaning, while 昆 supplies the sound. The original sense was waters mingling or flowing together, which extended to 'mix, blend, confuse.' Modern uses like 混乱 (chaos) and 混合 (to mix) preserve this core idea of things merging.