They see and show audible approval (4)
I believe the answer is:
eyes
'they see and' is the definition.
(I've seen this before)
'audible approval' is the wordplay.
'audible' becomes 'e' (I can't justify this - if you can you should believe this answer much more).
'approval' becomes 'yes' (I've seen this in another clue).
'e'+'yes'='EYES'
'show' is the link.
Can you help me to learn more?
(Other definitions for eyes that I've seen before include "Parts of needles" , "''Drink to me only with thine ...'' (Johnson)" , "Spots on a peacock's tail" , "Looks at - organs" , "Closely looks at" .)