Wiktionary
n. (context chemistry English) any analogue of a carboxylic acid, or general formula RC(=S)OH, RC(=O)SH or RC(=S)SH in which one or both of the oxygen has been replaced by sulfur
Wikipedia
Thiocarboxylic acids are organosulfur compounds related to carboxylic acids by replacement of one oxygen centre by sulfur. There are two possible tautomers, RC(S)OH and RC(O)SH, which are sometimes written as 'carbothioic O-acids' and 'carbothioic S-acids' respectively. The carbothioic S-acid tautomer RC(O)SH is far more common.
In the laboratory, the most common thiocarboxylic acid is thioacetic acid. A naturally occurring thiocarboxylic acid is 2,6-pyridinedicarbothioic acid, which functions as a siderophore. Thiocarboxylic acids are more acidic than the corresponding carboxylic acids.
Thiocarboxylic acids are typically prepared from the acid chloride:
CHC(O)Cl + KSH → CHC(O)SH + KCl