n. pl. per·fi·dies
1. Deliberate breach of faith; calculated violation of trust; treachery: "the fink, whose perfidy was equaled only by his gall" (Gilbert Millstein).
2. The act or an instance of treachery.
[Latin perfidia, from perfidus, treacherous : per-, to destruction; see PER- + fidēs, faith; see bheidh- 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.