一切經音義 27.178

27.178

唯然（上弋誰反說文諾也廣雅譍也禮記父召無諾先生召無諾唯而起鄭玄曰唯者譍之敬辭唯恭於諾又借音弋水反亦語辭也然順可也）。

Indeed so (唯然): The upper character is yishui [fanqie]. The Shuowen says: assent. The Guangya says: response. The Liji says: "When one's father calls, do not say nuo; when one's teacher calls, do not say nuo; respond with wei and rise." Zheng Xuan says: "Wei is a respectful term of response, more deferential than nuo." The borrowed pronunciation is also yishui [fanqie]; it is also a modal particle. 然 means compliant and acceptable.