di·a·base (dī'ə-bās') n. A dark-gray to black, fine-textured igneous rock composed mainly of feldspar and pyroxene and used for monuments and as crushed stone.
[French, partly from Greek diabasis, a crossing over (from diabainein, to pass through or over; see diabetes) and partly from diabase (dia-, two alteration of di-, from Greek di-; see di-1 + base, basis from Old French; see base1).]