huju, they don’t use it as a name for yogurt. you mean leaven (English word) not leben (originally Arabic, now used in Hebrew). I assume that Leben is derived from lavan, white, the color of milk. An etymology search told me that Leaven comes from French, levain, which derives from the French levare, meaning to raise up.
Wikepedia defines leben as curdled milk with the butter removed, also known as buttermilk.