It is generally believed that the meaning of “Yi (泗)” in the Book of Songs has been nasal fluids since Mao Heng, and has been explained from the perspective of borrowing, phonetic and ideographic word-formation, etc. However, there are still seven questions about the exact meaning of “Si (泗)”, which arouses different doubts about it. From the perspectives of handed-down documents and unearthed documents, variant relationships, literary meanings, contexts, dialects and so on, the word “Yi (泗)” of “Ti Si Pang Tuo (涕泗滂沱)” should be “Yi (㳑)” meaning that the water is full and flowing out. Furthermore, “Yi (泗)” has heterogeneous relationships with “Yi (益)”, “Yi (㳑)”, “Yi (溢)”, “Yi (洫)” and “Yi (泆)”, and has homologous relationships with “Ti (涕)”, “Yi (洟)” and “Ti (嚏)”, and has an isomorphic relationship with “Si (泗)” of “Si Shui (泗水)”. These relationships can be used to collate unearthed and handed-down documents.