Relating to speech sounds (8)
I believe the answer is:
phonetic
'relating to speech sounds' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for phonetic that I've seen before include "Representing what's said" , "Of spelling, corresponding to pronunciation" , "representing vocal sounds" , "(Spelling) as pronounced" , "Pinch toe (anag.)" .)