A dark-gray to black, fine-textured igneous rock composed mainly of feldspar and pyroxene and used for monuments and as crushed stone.
[From French diabase, originally meaning “diorite,” (now “basalt or gabbro lightly modified by metamorphism”), coined by French mineralogist Alexandre Brongniart (1770-1847), probably from Greek diabasis, a crossing over (from diabainein, to pass through or over; see DIABETES; the rock being so called because it is often found as intrusive sills and dikes in other rocks), or perhaps an alteration of an intended French *dibase (di-, two, from Greek di-; see DI-1 + base, basis, from Old French; see BASE1; the rock being so called in reference to feldspar and amphibole, two important constituent minerals of diorite).]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.