Sastamala.

Originally Saastamala (the short -a- might be an imitation of Swedish-language forms, but might also be variation found in local dialects), possibly originally from saasta (here “dirt, muck, mud”, but now “filth”) + -mala seen in many place names, possibly from the dialectal word malo (here “shore”) with later influence from the suffix -la commonly found in place names. The literal meaning of the name would thus be something like “mud(dy) shore”, referring likely to the western shores of the nearby lake Rautavesi. First attested in 1303 (as Sastamall). Originally this place name referred to a parish centered on the later municipality of Karkku. It was revived in 2009 to name the new municipality created when the then municipalities of Vammala (including Karkku subsumed in 1973), Mouhijärvi and Äetsä merged.