This paper revisits the meaning of “也孫 也速惕” (yisün yisüt) in Section 267 of The Secret History of the Mongols, offering a new interpretation along with supporting evidence. The term refers to the number of tribute items offered by Iluqu Burqan, ruler of Western Xia, to Činggis Qan (Genghis Khan) following the fall of his kingdom. Although most annotated editions translate yisün yisüt as “nine each” or “九九” (nine-nine), they rarely explain the reasoning behind this choice. One influential interpretation, proposed by Naka Michiyo (那珂通世), suggests that the term refers to gifts exchanged in sets of nine, or “nine each,” drawing on historical records of Khitan and Mongol practices. However, a closer look at the grammar challenges this view: in Mongolic languages, distributive numerals like “nine each” would require the form yisüged, not yisüt, since the suffix ~γad/ged must be attached to cardinal or base numbers. This grammatical point, together with cultural evidence, points toward an alternative interpretation. In Mongol tradition, the number nine carries a meaning of abundance and maximal extension, a symbolism that becomes even stronger when nine is multiplied by itself. Shamanistic rituals, historical records, and even legal codes all show examples of this symbolic use of repeated nines. Building on these examples, this study supports the interpretation of yisün yisüt as denoting “9x9,” which would best be understood as representing “81.”