A spacecraft that was spaceworthy was capable of spaceflight without malfunctioning.
In 2371, Miles O'Brien examined the specifications Benjamin Sisko brought from Bajor for a Bajoran lightship and felt they were not spaceworthy. He doubted such a ship could have traveled from Bajor to Cardassia. Sisko explained that he didn't want to sail for years, just build one and prove its spaceworthiness. O'Brien countered that he could do so with a computer model.
Later, Jadzia Dax questioned why Sisko made such a detailed replica, as it wasn't necessary to do so in order to test the the ship's spaceworthiness. Sisko agreed, but he still wanted everything to look right. (DS9: "Explorers")
In 2376, though she still had a ways to go, Tom Paris assured B'Elanna Torres that he could make the ship Alice spaceworthy. (VOY: "Alice")