Support at the seaside (5)
I believe the answer is:
shore
I believe this is a double definition.
'support' is the first definition.
(I know that shore is a more specific form of the action support)
'the seaside' is the second definition.
(I've seen this in another clue)
'at' acts as a link.
(Other definitions for shore that I've seen before include "Land beside sea, lake" , "Stay in" , "Land along the edge of sea or lake" , "Seafront" , "Land by water" .)