lapis

Lapis, lapidis, m., third declension. The stem is lapid-, so the nominative is the one form that hides it. Latin keeps three words apart where English mostly uses one: lapis is a stone you could lift or a worked block, saxum a rock or boulder, rupes a cliff face.

It also means a milestone, because Roman roads were measured by them, so ad tertium lapidem is "three miles out" and says nothing about masonry. In medieval technical prose lapis can be a gem or the alchemists' lapis philosophorum. English took lapidary, lapis lazuli and dilapidated, which literally means "having had its stones removed"; Spanish piedra and French pierre come from petra instead.