The term “surd” has diverse meanings across different fields, each rooted in its Latin origin from the word “surdus,” meaning “deaf” or “mute.”

  1. Mathematics: In this domain, “surd” refers to an irrational number, particularly one that cannot be expressed as a simple fraction and whose square root (or other root) cannot be simplified into a rational number. The term was originally used by the Arabic mathematician Al-Khwarizmi who described these numbers as “asl asamm” (deaf root in Arabic), which was later translated into Latin as “radix surda.” This reflects the concept that such numbers are, metaphorically speaking, “mute” or “silent” because they do not clearly “speak” to their exact values, being inexpressible in a straightforward fractional form.
  2. Phonetics: In linguistics, “surd” is used to describe voiceless sounds made without the vibration of the vocal cords. This definition again plays on the Latin meaning of “surdus,” as these sounds are “unvoiced” or “silent” in the sense that they lack the vocalic resonance that voiced sounds carry. In phonetics, surds contrast with sonants (or sonorants), which include any sound made with vocal cord vibration.

Thus, whether in the context of abstract mathematical concepts or the concrete mechanics of speech, the essence of “surd” remains consistent with its Latin roots, symbolizing aspects that are unspoken, indistinct, or inaudible.