笈 was the woven bamboo trunk a traveling scholar strapped to his back to carry his books and clothes — the Han-era image preserved in 史记 (Records of the Grand Historian) of 苏秦 'shouldering his 笈' to study with a master. The set phrase 负笈从师 ('shouldering one's book-box to follow a teacher') is still recognised today.
culture
Survives mainly in compounds: 秘笈 (mìjí, 'secret manual / hidden text', heavily used in wuxia novels for legendary kung fu manuals), 道笈 (Daoist scripture-box). Rarely seen alone in modern Chinese.
