(1):
(a.) Produced by the friction or rustling of the breath, intonated or unintonated, through a narrow opening between two of the mouth organs; uttered through a close approach, but not with a complete closure, of the organs of articulation, and hence capable of being continued or prolonged; - said of certain consonantal sounds, as f, v, s, z, etc.
(2):
(n.) A fricative consonant letter or sound. See Guide to Pronunciation, // 197-206, etc.