underlying

“We dug down to the underlying rock.”

“Old Yew, which graspest at the stones ⁠That name the under-lying dead, ⁠Thy fibres net the dreamless head, Thy roots are wrapt about the bones.”

“Points and straight lines are underlying elements of geometry.”

“Finding a successful treatment for Alzheimer’s faces two major hurdles: the first being we still don’t know enough about the disease’s underlying biology.”

“Many nursery rhymes have an underlying meaning.”