https://doi.org/10.1351/goldbook.T06352
Compounds in which one or both oxygens of a carboxy group have been replaced by divalent sulfur $\ce{RC(=O)SH}$ or $\ce{RC(=S)OH}$ monothiocarboxylic acids, $\ce{RC(=S)SH}$ dithiocarboxylic acids.