Link
Also, even more interesting:
The ship was colloquially known as a "Super Star Destroyer" because the Imperial Navy listed it as a "Super-class Star Destroyer" in budget requests to hide its true nature from the Imperial Senate. Even the ship's size was reported incorrectly to conceal its role from oversight committees. Although the official designation was changed by the time the Executor was operational, the phrase "Super Star Destroyer" stuck, and it was even applied to later vessels such as the Sovereign-class and Eclipse-class.