Grosuplje was first attested in written sources in 1136 as
Groslupp (and as
Grasslupp in 1220–50, and
Grazlup in 1249). The settlement is known as
Grasuple in the local dialect. The etymological origin of the name is unclear. One theory derives it from
*Graslupoje (selo/poľe)—literally, 'wet (village/field)', from the adjective
*graslupъ. Another theory derives the name from
Lombard *grass(ah)lauffja 'rapids' but is undermined by the lack of fast-flowing water in the area. Yet another theory derives it from the hypothetical Lombard name
*Graslupus borrowed into Slavic as
*Groslupъ, whereby
*Groslupľe selo would literally mean 'Groslupъ's village'. In the past the German name was
Großlupp. ==Mass grave==