someone from whom you are descended (but usually more remote than a grandparent)
"Our family recently visited the ancestral home where our great-grandparents once lived."
One from whom a person is descended, whether on the father's or mother's side, at any distance of time; a progenitor; a forefather.
"My great-grandmother told me that her ancestor who sailed across the ocean in 1847 was actually a skilled carpenter before he left home."
To be an ancestor of.
"My great-grandmother was a direct ancestor of my entire family tree, tracing back to the village where we all originated."