Zuun remained a small, sparsely populated hamlet of Sint-Pieters-Leeuw until the 19th century. This name is due to the Zuunbeek, one of the most important tributaries of the Senne. The Zuunbeek is barely 9 km long and has no unambiguous source. It is created by the confluence of thirteen different rivers in the central Pajottenland. On the border between the municipalities of Pepingen and Sint-Pieters-Leeuw, the newly formed watercourse is named Zuunbeek after the confluence of Beringen and Karenbergbeek. In the former café "in de Blauw" in Oudenaken, the Zuunbeek also catches water from the Molenbeek in Lennik. Many of the waters of Leeuwse also flow into the Zuunbeek and eventually the large stream crosses the Brussels-Charleroi canal via a siphon. Shortly afterwards, it flows into the Senne at the border with Drogenbos and Anderlecht through tunnels under the Brussels Ring.

The name 'Zuun' is associated with the Celtic language and the words 'Sinde' or 'Senna' meaning 'stream'. From the end of the 11th century until 1776, other spellings were in use: Sone, Soniam, Zuene, Zeune and Zuen. Preserved Ferrari maps from the Austrian era prove that the Zuunbeek was surrounded by the two main roads connecting Brussels until the 18th century. It can therefore be said that the Zuunbeek played an important role in the creation of the old village centre and St. Peter's Church on a hill on the ice rink.