Experts listened to ordinary language (4)
I believe the answer is:
pros
'experts' is the definition.
(I've seen this in other clues)
'listened to ordinary language' is the wordplay.
'listened to' indicates a 'sounds like' (homophone) clue.
'ordinary language' becomes 'prose' (I've seen this before).
'prose' is a homophone of 'PROS'.
(Other definitions for pros that I've seen before include "Persons with knowledge and skill" , "Yes votes" , "Sportsmen who are paid" , "Positive arguments" , "Arguments in favour" .)