Definition - The inability to say sibilant sounds.

Example -

"Thuffering thuckatash."
"Thuffering thuckatash."

Warner Brother's Sylvester the Cat is sigmatic. For example, he can't say "Suffering Succotash."

Etymology -
The word derives from the Greek sigma, the name for the Greek equivalent of the letter S.

Oxford English Dictionary -
Its first citation is from 1888:
"Lisping, or *Sigmatism, is the most common form of stammering. It consists of giving s a wrong sound, usually that of th, by carrying the tip of the tongue too far forward, so as to touch the upper teeth."
(A. H. Buck Reference Handbook of Medical Science, VI. 617/1)

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