the.com/starter

means A fermented flour-and-water culture, alive with wild yeast and bacteria, used to leaven bread instead of commercial yeast.

from Simply agent-noun logic: something that 'starts' things, from Old English 'styrtan,' to leap or rush — the same root behind 'start' meaning a sudden movement. Bakers borrowed the plain English word for the thing that gets the dough going, probably sometime after commercial yeast became common enough that the old wild-fermented method needed a name to distinguish it. No hidden story — just a culture that starts the rise, called, honestly, a starter.