From Tolkien Gateway

Mundburg was the name given to Minas Tirith by the Rohirrim of Rohan in their own tongue.[1] It presumably comes from the Old English mundbeorg, meaning "Protecting Hill". The name of the "Mounds of Mundburg" comes from this title.[2]

Other versions of the legendarium[edit]

On an unfinished sketch, Tolkien has written the names Stanburg (Old English) and Steinborg (Old Norse) both meaning "Stone City".[3]