A quantity which can not be expressed by rational numbers; thus, sqrt(2) is a surd.
2.
(Phon.) A surd element of speech. See Surd, a., 4.
adjective
Surd adj.
1.
Net having the sense of hearing; deaf. (Obs.) "A surd... generation."
2.
Unheard. (Obs.)
3.
(Math.) Involving surds; not capable of being expressed in rational numbers; radical; irrational; as, a surd expression or quantity; a surd number.
4.
(Phonetics) Uttered, as an element of speech, without tone, or proper vocal sound; voiceless; unintonated; nonvocal; atonic; whispered; aspirated; sharp; hard, as f, p, s, etc.; opposed to sonant.
... which covered the floor. Even then there was no uproar, no rush or push, no sharp cries or frenzied shouting; but from the crowd, which was largely made up of elderly men, there rose a sort of surd, rich hum, deepening ever, and never breaking into a shriek of torment or derision. It was not histrionic, and yet for its commercial importance it was one of the most moving spectacles which could offer itself to the eye in ... — Seven English Cities • W. D. Howells
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