Look closely to see the pier's sound (4)
I believe the answer is:
peer
'look closely' is the definition.
(I've seen this in another clue)
'the pier's sound' is the wordplay.
'sound' indicates a 'sounds like' (homophone) clue.
'pier' is a homophone of 'PEER'.
'to see' is the link.
(Other definitions for peer that I've seen before include "Gaze" , "Look dimly at lord" , "Person of equal standing" , "Equal -- look searchingly" , "Fellow" .)