Wader has to keel over after sun (5)
I believe the answer is:
stilt
'wader' is the definition.
(a wading bird)
'to keel over after sun' is the wordplay.
'to keel over' becomes 'tilt' (to keel over is to tilt or lean).
'after' is a charade indicator (letters next to each other).
'sun' becomes 's'.
'tilt' put after 's' is 'STILT'.
'has' is the link.
(Other definitions for stilt that I've seen before include "Flier" , "Stout pole with a foot rest -- wading bird" , "Long-legged wader" , "Walking pole; wader" , "Long-legged bird" .)