adj. Net having the sense of hearing; deaf. Unheard. (Math.) Involving surds; not capable of being expressed in rational numbers; radical; irrational; as, a surd expression or quantity; a surd number.
- (Phonetics) Uttered, as an element of speech, without tone, or proper vocal sound; voiceless; unintonated; nonvocal; atonic; whispered; aspirated; sharp; hard, as f, p, s, etc.; - opposed to sonant.
- n. (Math.) A quantity which cannot be expressed by rational numbers. (Phon.) A surd element of speech. See Surd, a.