Here's the explanation of your name: If you look in records from the 16th century in the area above Lake Thun in Bern (now Canton Bern in Switzerland), you will find the name Ösch.Most of the names at the time were either occupations, descriptions of natural features, or locations. This one was natural: the ash tree, which was very common. I found the name in Steffisburg records from the 1530s, but you could probably find it in many locations. In the local dialect, the umlaut (double dot) didn't always give the vowel a long sound; for instance, my family name, Stücker, actually came out 'Stecker,' and that is the way it was spelled when my illiterate ancestors moved up to Lorraine and pronounced it to municipal clerks. Part of the Oesch family became Amish Mennonite, part did not.