The Valiant is a dropped name

Original designs for the USS Defiant for Star Trek: Deep Space Nine called for a "beefed-up" runabout-type ship, but this gave way to a full-fledged starship design, initially called Valiant. This name was dropped out of fear that it would conflict with Star Trek: Voyager and its titular starship, also beginning with a "V". For a brief time it was considered to retain Valiant as the name of the class: but dialog in "The Search" and the ship's dedication plaque firmly establish the Defiant as the pathfinder.