1. Mathematics An irrational number, such as √2.
2. Linguistics A voiceless sound in speech.
Voiceless, as a sound.
[Medieval Latin surdus, speechless, surd (translation of Arabic (jaḏr) 'aṣamm, deaf (root), surd, translation of Greek alogos, speechless, surd), from Latin.]
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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.