Defiant, USS - Federation starship on the science fiction series STAR TREK: DEEP SPACE NINE/SYN/1993-99. The USS Defiant was originally designed to fight a ruthless race of cybernetic beings called The Borg (from the Delta Quadrant), but was later given to Star Fleet Commander Captain Sisko (Avery Brooks) as a defense against another Federation threat, The Dominion, (from the Gamma Quadrant). Officially the Defiant was classed as an escort ship; unofficially it was a warship.

Stationed at space station Deep Space Nine, the Defiant protected the surrounding space including the planet Bajor and a nearby wormhole, a strategic shortcut in space to other unexplored parts of the galaxy.

To further protect the Defiant from straying enemy eyes, it was secretly equipped with a Romulan invisibility cloaking devices that screened the ship from radar-like scans of hostile ships.