Sibilant \Sib"i*lant\, a. [L. sibilans, -antis, p. pr. of sibilare to hiss: cf. F. sibilant.]

Making a hissing sound; uttered with a hissing sound; hissing; as, s, z, sh, and zh, are sibilant elementary sounds. -- n. A sibiliant letter.

Source: Webster's Revised Unabridged Dictionary (1913)