Compounds in which one or both oxygens of a carboxy group have been replaced by divalent sulfur
RC(=O)SH or
RC(=S)OH monothiocarboxylic acids,
RC(=S)SH dithiocarboxylic acids.
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1372 (https://doi.org/10.1351/pac199567081307)