Róuyīn (-)
original: 揉音
Literal translation: 揉: "(to) rub / knead"; 音: "sound / tone"; Defined by Wong as "vibrato".
Wong, Samuel Shengmiao: Qi’ - An instrumental guide to the Chinese orchestra. Singapore, 2005, p.139, 143.
汉英词典 (Hàn Yīng cídiǎn) / A Chinese-English dictionary. 北京 [Běijīng], 1985, p.578 & 826.