We hear aristocrat is seaside attraction (4)
I believe the answer is:
pier
'seaside attraction' is the definition.
(structure by the sea)
'we hear aristocrat' is the wordplay.
'we hear' shows a homophone (sound like).
'aristocrat' becomes 'peer' (peer is a kind of aristocrat).
'peer' is a homophone of 'PIER'.
'is' acts as a link.
(Other definitions for pier that I've seen before include "Seaside attraction" , "Mole, wall between windows" , "Landing-stage or promenade" , "Support member" , "Seaside platform" .)