Comments of chapter undefined of Fourth Scourge of Star Wars

Definitely Star Destroyer. They have been called Venator-class Star Destroyers for more than a decade and we aren't talking about something from a different franchise that is being reclassified into a Star Wars fleet. Informally you could call them a Venator battlecruiser, but Venator-class battlecruiser feels too formal to be correct as a battlecruiser is also a proper designation for 2-5km ships while 1-2km was for Star Destroyers in the Clone Wars era.