捷思 (jié sī) is a literary and somewhat formal noun meaning 'quick wit' or 'sharp, agile thinking' — the ability to grasp ideas rapidly and respond cleverly in the moment. The first character 捷 (jié) means 'swift, nimble, victorious', often implying efficiency and success; the second character 思 (sī) means 'thought, thinking, reflection'. Together, they evoke mental agility — not just speed, but insightful, well-timed cognition.

This term appears most often in written Chinese, such as essays, biographies, or descriptions of intelligent historical figures or fictional characters. It’s rarely used in casual speech; native speakers more commonly say 聪明 (cōngmíng) or 反应快 (fǎnyìng kuài) for everyday 'quick-wittedness'. 捷思 carries a refined, almost classical tone and suggests intellectual elegance rather than mere quickness.