surd
noun /sɜːd/
/sɜːrd/
(also irrational number)
(mathematics)- a number, for example π or the square root of 2, that cannot be expressed as the ratio of two whole numbersWord Originmid 16th cent.: from Latin surdus ‘deaf, mute’; as a mathematical term, translating Greek (Euclid) alogos ‘irrational, speechless’, apparently via Arabic jid̲r aṣamm, literally ‘deaf root’.