Sigmatism, by another name (4)
I believe the answer is:
lisp
'sigmatism by another name' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lisp that I've seen before include "peech impediment" , "Be unable to pronounce S" , "Have difficulty pronouncing `s'" , "speak imperfectly" , "Non-standard pronunciation" .)