trithiophosphate

from The Century Dictionary.

• noun A salt corresponding to the hypothetical trithiophosphoric acid, H₃PS₃O, which may be viewed as ordinary phosphoric acid having three of its four atoms of oxygen replaced by sulphur. This acid is not itself known in the free state.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry Any thiophosphate in which three oxygen atoms have been replaced by sulfur