Late-Táng / early-Sòng scholar-official and philologist, zì Dǐngchén 鼎臣, of Guǎngling (modern Yangzhou). Brother of Xú Kǎi 徐鍇 (the two are conventionally referred to as the “Two Xús” 二徐 in Chinese paleography). Held high office under the Southern Táng (rising to Yùshǐ dàfū and Lìbù shàngshū); after the Sòng absorption of the Southern Táng in 975, served the Sòng court as Sànjì chángshì. His monumental contribution is the imperially-commissioned revision of Xǔ Shèn’s 許愼 Shuōwén jiězì KR1j0018 (Yōngxī 3 / 986), the recension known as DàXúběn 大徐本 — adding fǎnqiè readings from Sūn Miǎn’s Tángyùn, supplying the xīnfùzì 新附字, splitting the original 14 piān into 30 juàn, and adding editorial ànyǔ. He also produced the Shuōwén jiězì zhuànyùnpǔ KR1j0021 (with his brother), a phonetically-organized re-presentation of the Shuōwén lemmata, and was a notable seal-script calligrapher in his own right. CBDB lifedates 916–991, in agreement with the Sòngshǐ biography (juàn 441).