1. Of, relating to, or resembling rock, especially in hardness; stony.
2. Of or relating to the very dense, hard portion of the temporal bone that forms a protective case for the inner ear.
[Middle English, from Old French petros, from Latin petrōsus, rocky, from petra, rock, from Greek petrā; see per-2 in the Appendix of Indo-European roots.]
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Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.