Pentath III was the inhabited third planet in the Pentath system. This was a Cardassian planet.

Pentath III was one of many planets in the Cardassian Union whose infrastructure was devastated by the Klingon invasion of 2372. An outbreak of Rudellian plague there prompted the Detapa Council to dispatch several relief convoys to the planet. Due to the lack of Cardassian fleet resources, the Council requested Starfleet escorts for the convoys. The USS Defiant was one of the starships assigned to this mission. (DS9: "Rules of Engagement")

This planet was only mentioned in dialogue.
According to the script, the pronunciation for Pentath was "PEN-tath". [1]