Also 6–7 surde. [ad. L. surdus (in active sense) deaf, (in pass. sense) silent, mute, dumb, (of sound, etc.) dull, indistinct.
The mathematical sense ‘irrational’ arises from L. surdus being used to render Gr. ἄλογος (Euclid bk. x. Def.), app. through the medium of Arab. açamm deaf, as in jaðr açamm surd root.]
A. adj. 1. Math. Of a number or quantity (esp. a root): That cannot be expressed in finite terms of ordinary numbers or quantities: = IRRATIONAL A. 3. (Cf. INCOMMENSURABLE 1.)
1551. Recorde, Pathw. Knowl., II. Pref. Quantitees partly rationall, and partly surde.
1571. Digges, Pantom., IV. vi. X ij. Tetraedrons side being rationall, the Axis is surde, and it beareth proportion to the side as 1. to √ 24.
1623. Bp. Andrewes, XCVI Serm., xvi. (1629), 156. Such surd numbers, such fractions we shall meet with, we shall not tell how or when to gett through.
1659. Leybourn, Arith., IV. iv. (1660), 339. There are many sorts of surd roots, some are simple,… others are compound.
1793. Hutton, Course Math. (1806), I. 80. The cube root of 8 is rational, being equal to 2; but the cube root of 9 is surd or irrational.
1861. T. Lund, J. Wood’s Elem. Alg., 97. An equation may be cleared of a surd by transposing the terms so that the surd shall form one side, and the rational quantities the other, and then raising both sides to that power which will rationalize the surd.
† 2. Deaf. Obs. rare.
1682. Sir T. Browne, Chr. Mor., III. § 6. He … may … apprehend how all Words fall to the Ground, spent upon such a surd and Earless Generation of Men.
1819. H. Busk, Vestriad, I. 763. Whistlings, whizzes, strike thy senses surd.
3. fig. † a. Not endowed with sense or perception; insensate, unintelligent. Obs.
In quot. 1668, deficient in perception, dull: cf. c.
1601. Holland, Pliny, XXVII. xiii. II. 292. Those medicinable vertues … bestowed vpon those surd and senslesse hearbs.
1668. H. More, Div. Dial., II. xxvi. (1713), 174. My palate is something more surd and jacent.
a. 1676. Hale, Prim. Orig. Man., I. ii. (1677), 44. Neither Chance nor surd or inanimate Nature could be the Efficient of such a Being.
b. Irrational, senseless, stupid. (In recent use only as a direct figure from 1.)
1610. A. Cooke, Pope Joan, 60. Rupertus,… commonly called Grosthead. A great Philosopher … though it pleased your Pope Innocentius the fourth, to call him old foole, surd, and absurd companion.
1625. Jackson, Creed, V. xlvii. § 6. Their irrational and surd conceits of scripture’s sense.
1642. H. More, Song of Soul, II. i. I. vii. And foul blasphemous belch from their surd mouth resounds.
1863. M. Pattison, Ess., xvii. (1889), II. 295. The surd and irrational complexion of that party is due to the circumstance that all its best minds went from it.
1891. H. Jones, Browning as Teacher, 24. The problems have a surd or irrational element in them.
† c. Not clearly or keenly perceived, dull; stingless. Obs.
1597. A. M., trans. Guillemeau’s Fr. Chirurg., 48/2. The dolour not so pungent and sharp, but somwhat more surde and benumde. Ibid. (1599), trans. Gebelhouer’s Bk. Physicke, 202/2. Take … oyle of Hempeseede and surde nettles.
† d. Conveying no sense, meaningless, Obs.
1605. Bacon, Adv. Learn., II. xxv. § 4. The Ceremonies of Idolatrie and Magicke that are full of Non-significants and surde characters.
4. Phonetics. Uttered without vibration of the vocal cords; voiceless, ‘breathed’: opposed to SONANT. (Cf. F. sourd.)
1767. Ess., in Ann. Reg., 194/1. Mute, surd, and nasal syllables.
1773. Kenrick, Dict., Gram. Eng. Lang., 27. All our modes of articulation, whether surd or vocal.
1863. Max Müller, Sci. Lang., Ser. II. vii. (1868), 297. No longer mere interjections … uncertain between surd, sonant, or aspirated enunciation.
1887. Cook, trans. Sievers’ O. E. Gram., 99. P is a surd labial stop.
5. Arabic Gram. (trans. Arab. açamm lit. deaf). Applied to verbs in which the second and third letters of the root are the same.
1776. Richardson, Gram. Arab. Lang., III. v. 97. The Surd verb, so called because the last radical is not heard, coalescing with the second by Teshdid. Ibid. (1777), Arab.-Pers. Dict., 138. [Arabic] el’ asammu The surd or teshdid conjugation of Arabick verbs.
1823. W. Price, Gram. 3 Oriental Langs., 112. Conjugation of the Surd Verd, [Arabic] della, he ogled.
B. sb. 1. Math. A surd or irrational number or quantity, esp. root: see A. 1.
1557. Recorde, Whetst., L l iij. Those nombers are not Surde nombers properly, but sette like Surdes. As the Square roote of .4.
1571. Digges, Pantom., IV. vii. X ij b. The Hexaedrons comprehending Spheres Dimetiente beeing rationall, his Axis is a surde.
1674. Jeake, Arith. (1696), 294. Surdes are Simple or Compound, Integral or Fracted.
1743. Emerson, Fluxions, 83. Any Power of the Quantity under the Vinculum (in any Binomial or Trinomial Surd).
1869. ‘Lewis Carroll,’ Phantasmagoria, etc., 110.
| Yet what are all such gaieties to me | |
| Whose thoughts are full of indices and surds? |
attrib. 1869. J. H. Smith, Elem. Algebra, 164. Surds of the same order are those for which the root-symbol or surd-index is the same.
fig. 1856. Ferrier, Inst. Metaph., IV. (ed. 2), 143. It becomes the absolutely incogitable—a surd.
1877. E. Caird, Philos. Kant, II. xv. 551. The old difficulty … that reappears always as the inexplicable surd of his philosophy.
2. Phonetics. A speech-sound uttered without ‘voice’; a ‘breath’ consonant: see A. 4.
1789. E. Darwin, Bot. Gard., II. 60. Weighs with nice ear the vowel, liquid, surd, And breaks in syllables the volant word.
1842. Proc. Philol. Soc., I. 7. The tenues (otherwise surds, or whisper-letters).
1871. Public Sch. Lat. Gram., 7. The use of C as a surd made K superfluous.
