Definition of surd in English:


Pronunciation /sərd/


  • 1Mathematics
    (of a number) irrational.

  • 2Phonetics
    (of a speech sound) uttered with the breath and not the voice (e.g. f, k, p, s, t).


  • 1Mathematics
    A surd number, especially the irrational root of an integer.

    ‘They were learning about surds in maths, supposedly one of the hardest subjects.’
    • ‘I don't care about rationalising denominators with surds in them, and I don't care that by using maths induction you can prove many equations to be right or wrong.’
    • ‘In the conventional school education in India, we are asked to do some problems involving surds (radicals).’
  • 2Phonetics
    A surd consonant.


Mid 16th century from Latin surdus ‘deaf, mute’; as a mathematical term, translating Greek (Euclid) alogos ‘irrational, speechless’, apparently via Arabic jiḏr aṣamm, literally ‘deaf root’. surd (sense 2 of the adjective) dates from the mid 18th century.