What is making a hissing sound; uttered with a hissing sound; hissing; as, s, z, sh, and zh, are sibilant elementary sounds. -- n. A sibiliant letter called?

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. (Webster's 1913.)

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