In ancient Roman religion, a lūcus ([ˈɫ̪uː.kʊs], plural lūcī) is a sacred grove. Lucus was one of four Latin words meaning in general "forest, woodland, grove" (along with nemus, silva, and saltus), but unlike the others it was primarily used as a religious designation. Servius defines the lucus as "a large number of trees with a religious significance," as distinguished from the silva, a natural forest, and a nemus, an arboretum that is not consecrated. A saltus usually implied a wilderness area with varied topographical features.