Orientine acid

Orientine acid was a very strong acid. It was capable of burning through almost anything except for a certain crystal in which it was normally contained.

In 2269, James T. Kirk threatened to pour orientine acid on an examination table in the sickbay of the USS Enterprise, when he suspected that the table was actually the Vendorian shapeshifter. (TAS: "The Survivor")

According to the original script, this was pronounced "Oree-EN-teen". [1] It is described there as a "purple fluid" in a "glittering crystal" vial.