Entelior IV is the fourth planet of the Alpha Quadrant's Entelior star system. The planet has a planetary ring and an inhospitable environment.
In 2317, Zeeren was waiting for Strolt on Entelior IV. (ST - Tales from the Captain's Table short story: "Iron and Sacrifice")
In 2362, the USS Okinawa and the USS Assurance engaged Tzenkethi warships near Entelior IV. The Assurance was critically damaged after one of the Tzenkethi vessels launched a suicide run against it and the starship was pulled into Entelior IV's atmosphere. The Assurance was saved from destruction after Benjamin Sisko's plan to use three shuttlecraft from the Okinawa to slow its descent using tractor beams was successful. (ST - Typhon Pact novel: Rough Beasts of Empire)
A Federation colony was later established on the planet, but was attacked and destroyed by the Borg during their invasion of the Federation in 2381. Starfleet soon began to evacuate the colonists to Laskitor III. (ST - Typhon Pact novel: Plagues of Night)