Surd

Part of speech: noun

Pronunciation: /sɜːd/

Definitions

1. A numerical expression that involves a root, which represents an unresolvable square root or cube root within mathematics
2. Referring to a radical expression that remains unresolved as it cannot be simplified into a rational number or whole number
3. A number expressed as a root that cannot be simplified into a fraction or whole number

Etymology: The surd in mathematics began as a mistranslation of a Greek idea. Euclid used "alogos," meaning "irrational" but also "speechless," for quantities that could not be expressed as a ratio of whole numbers. When Arabic mathematicians translated this, the phrase they used was "jiḏr ʔaṣamm," or "deaf root," and the Latin "surdus," meaning "deaf" or "mute," was then chosen as the equivalent. The English term, first recorded in the mid 16th century, carries that metaphor directly: an irrational root was a root that could not "speak" in terms of ordinary numbers. The word's other meaning came much later. In the 18th century it was adopted in phonetics for sounds produced without vocal-cord vibration, such as the "s" in "sit," which is a deaf sound in the literal sense. The two senses therefore share a root but reached English by different routes, one through Greek mathematics and one through the description of speech.

Synonyms: irrational, non-rational

Antonyms: rational