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
1545-55; < Latin surdus dull-sounding, mute, deaf
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
Word Origin and History for surd
adj.

1550s, "irrational" (of numbers), from Latin surdus "unheard, silent, dull," possibly related to susurrus "a muttering, whispering" (see susurration). The mathematical sense is from the use of Latin surdus to translate Arabic (jadhr) asamm "deaf (root)," itself a loan-translation of Greek alogos, literally "speechless, without reason" (Euclid book x, Def.). In French, sourd remains the principal word for "deaf."