adj. & n.
--adj.
1. Math. (of a number) irrational.
2 Phonet. (of a sound) uttered with the breath and not the voice (e.g. f, k, p, s, t).
--n.
1. Math. a surd number, esp. the root of an integer.
2 Phonet. a surd sound.
Etymology: L surdus deaf, mute: sense 1 by mistransl. into L of Gk alogos irrational, speechless, through Arab. jadr asamm deaf root