Relating to speech sound (8)
I believe the answer is:
phonetic
'relating to speech sound' is the definition.
(I know this)
This is all the clue.
(Other definitions for phonetic that I've seen before include "(Spelling) as pronounced" , "Pinch toe (anag.)" , "Relating to speech sounds" , "Relating to the sounds of spoken language" , "representing vocal sounds" .)