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surd

[surd] /sɜrd/
adjective
1.
Phonetics. voiceless (opposed to sonant).
2.
Mathematics. (of a quantity) not capable of being expressed in rational numbers; irrational.
noun
3.
Phonetics. a voiceless consonant (opposed to sonant).
4.
Mathematics. a surd quantity.
Origin
1545-1555
1545-55; < Latin surdus dull-sounding, mute, deaf
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for surd

surd

/sɜːd/
noun
1.
(maths) an expression containing one or more irrational roots of numbers, such as 2√3 + 3√2 + 6
2.
(phonetics) a voiceless consonant, such as (t)
adjective
3.
of or relating to a surd
Word Origin
C16: from Latin surdus muffled
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for surd
surd
1551, "irrational" (of numbers), from L. surdus "unheard, silent, dull," possibly related to susurrus "a muttering, whispering" (see susurration). The mathematical sense is from the use of L. surdus to translate Ar. (jadhr) asamm "deaf (root)," itself a loan-translation of Gk. alogos, lit. "speechless, without reason" (Euclid bk. x, Def.). In Fr., sourd remains the principal word for "deaf."
Online Etymology Dictionary, © 2010 Douglas Harper
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