續一切經音義 5.141

5.141

指擘（下補革反三蒼云擘大拇指也陸氏釋文云手足大指俱名擘也今經云大如指擘即形段如大拇指也）。

Thumb [指擘] (The second character has the fanqie phonetic spelling 補 + 革; the Sancang says that bo is the big thumb; Lu Deming's Jingdian Shiwen says: "The big digits of both the hands and feet are named bo"; now the sūtra says "as large as a thumb", meaning of the size and dimension of a big thumb).