1
- Mathematics (of a number) irrational【数】不尽根的。
2
- Phonetics (of a speech sound) uttered with the breath and not the voice (e.g. f, k, p, s, t)【语音】清音的（如f, k, p, s, t）。
1
- Mathematics a surd number, especially the irrational root of an integer【数】不尽根（尤指整数的不尽根）。
2
- Phonetics a surd consonant【语音】清音。
词源
mid 16th cent.: from Latin surdus 'deaf, mute'; as a mathematical term, translating Greek (Euclid) alogos 'irrational, speechless', apparently via Arabic jiḏr aṣamm, literally 'deaf root'. Sense 2 dates from the mid 18th cent.