急剧
jí jù · HSK 7
rapid
📉⚡ 急 (urgent) + 剧 (intense/severe) = change that's both urgent and steep, i.e. rapid
急 carries the sense of hurried or urgent; 剧 means intense or severe (same 剧 as in drama). Together they describe a change that happens fast and sharply, like a sudden drop or spike.
急 — heart radical 心 + 及 (reach)
A semantic-phonetic compound: the heart radical 心 supplies the meaning (an emotional state) while 及 ('to reach, catch up') gives the sound. Originally it depicted a racing, anxious heart — hence the modern senses 'urgent,' 'hurried,' and 'impatient.'
剧 — 豦 (tiger+pig) + 刂 knife radical
Originally written 劇, a phono-semantic compound: 豦 (jù, a fierce beast) gives the sound, while 刂 (knife) suggests intensity or cutting action. The original meaning was 'severe' or 'intense,' later extended to 'drama/play' since theatrical performances were dramatic and intense. 剧 is the simplified form.