• WordNet 3.6
    • adj surd produced without vibration of the vocal cords "unvoiced consonants such as `p' and `k' and `s'"
    • n surd a consonant produced without sound from the vocal cords
    • ***
Webster's Revised Unabridged Dictionary
    • Surd A quantity which can not be expressed by rational numbers; thus, √2 is a surd .
    • Surd (Phon) A surd element of speech. See Surd a., 4.
    • Surd (Math) Involving surds; not capable of being expressed in rational numbers; radical; irrational; as, a surd expression or quantity; a surd number.
    • Surd Net having the sense of hearing; deaf. "A surd . . . generation."
    • Surd Unheard.
    • Surd (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. See Guide to Pronunciation, §§169, 179, 180.
    • ***
Century Dictionary and Cyclopedia
    • surd Not having the sense of hearing; deaf.
    • surd That cannot be discriminated by the ear (?).
    • surd In mathematics, not capable of being expressed in rational numbers: as, a surd expression, quantity, or number. See II., 1.
    • surd In phonetics, uttered with breath and not with voice; devoid of vocality; not sonant: toneless: specifically applied to the breathed or non-vocal consonants of the alphabet. See II., 2.
    • surd Meaningless; senseless.
    • n surd In mathematics, a quantity not expressible as the ratio of two whole numbers, as √ 2, or the ratio of the circumference of a circle to the diameter. The name surd arises from a mistranslation into Latin of the Greek ἄλογος, which does not mean ‘stupid’ or ‘unreasonable,’ but ‘inexpressible.’
    • n surd In phonetics, a consonantal sound uttered with breath and not with voice; a non-sonant consonant; a non-vocal alphabetic utterance, as p, f, s, t, k, as opposed to b, v, z, d, g, which are sonants or vocals.
    • surd To render dim or soft; mute.
    • surd Containing or involving a surd : thus [1 + ½] ½ is a surd expression but not a surd, since 1 + ½ is not a rational expression.
    • n surd In mathematics: An indicated root whose value is irrational, but whose radicand is rational, as ½. A surd is quadratic, cubic, of order n, according as its exponent is ½, ⅓, 1/n;.
    • ***
Chambers's Twentieth Century Dictionary
    • adj Surd surd (alg.) involving surds: produced by the action of the speech organs on the breath (not the voice), as the 'hard' sounds k, t, p, f, &c.: deaf:
    • n Surd (alg.) a quantity inexpressible by rational numbers, or which has no root
    • adj Surd surd (obs.) unheard, senseless
    • ***


  • Lewis Carroll
    “Yet what are all such gaieties to me whose thoughts are full of indices and surds?”


Webster's Revised Unabridged Dictionary
L. surdus, deaf (whence the meaning, deaf to reason, irrational), perhaps akin to E. swart,. Cf. Sordine
Chambers's Twentieth Century Dictionary
L. surdus, deaf.


In literature:

Do you mean to say that you are not able to tell me what a surd is?
"A Portrait of the Artist as a Young Man" by James Joyce
Since the fraction is infinite it cannot be commensurable and therefore its value is a quadratic surd number.
"Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 2" by Various
Which is doub-ly ab-surd!
"John March, Southerner" by George W. Cable
The second of numbres and quantitees surde or irrationall.
"The Path-Way to Knowledg" by Robert Record
"Darwin, and After Darwin (Vol 3 of 3)" by George John Romanes
According to the view of knowledge as representation of an eternal content, the psychical is a mere logical surd.
"Studies in Logical Theory" by John Dewey
No word can end in an unaspirated surd consonant.
"Encyclopaedia Britannica, 11th Edition, Volume 15, Slice 6" by Various