The word "kremlin" comes from an old Russian word meaning what?

Kremlin, (Russian "kreml", formerly "kremnik"), was a central fortress or citadel in medieval Russian cities, usually located at a strategic point along a river and separated from the surrounding parts of the city by a wooden—later a stone or brick—wall with ramparts, a moat, towers, and battlements. Several capitals of principalities (e.g., Moscow, Pskov, Novgorod, Smolensk, Rostov, Suzdal, Yaroslavl, Vladimir, and Nizhny Novgorod) were built around old kremlins, which generally contained cathedrals, palaces for princes and bishops, governmental offices, and munitions stores. The original Moscow Kremlin dates from 1156 and it was founded by the Russian ruling dynasty of Rurikids. The oldest remaining section dates from the 14th–15th century and is located in the southwest.

Moscow is the best known of the kremlins and includes five palaces, four cathedrals, and the enclosing Kremlin Wall with Kremlin towers. In addition, within this complex is the Grand Kremlin Palace that was formerly the Tsar's Moscow residence. The complex now serves as the official residence of the President of the Russian Federation and as a museum with almost 3 million visitors in 2017.

The Kremlin overlooks the Moskva River to the south, Saint Basil's Cathedral and Red Square to the east, and the Alexander Garden to the west.