Wolfgang, Alice, et al:

According to Getty Thesaurus of Geographic Names there is a river named Mosson in Hérault department, Languedoc-Roussillon region of France. (The spellings mossen, mossem, and mossing turned up nothing.)

A Google search showed that there is a chateau called Le château de la Mosson on the banks of the Mosson in Montpellier.

There is a soccer stadium called La Mosson, named after the river.