急性
jíxìng · HSK 7
acute (of diseases)
🚑 急 urgent + 性 -nature = urgent-natured illness = acute
急 means urgent or hurried; 性 is the -ness suffix marking a quality or type. An acute disease is the urgent-natured kind: it comes on fast and hits hard, opposite of the slow 慢性 (chronic).
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.'
性 — heart radical 忄 + 生 (life/birth)
性 is a semantic-phonetic compound. The heart radical 忄 supplies the meaning, pointing to inner feelings or innate qualities, while 生 ('birth, life') gives the sound and hints at what one is born with. It originally meant 'inborn nature' and later extended to 'character,' 'gender,' and 'sex.'