Reject outcast on return (5)
I believe the answer is:
repel
'reject' is the definition.
(I've seen this before)
'outcast on return' is the wordplay.
'outcast' becomes 'leper' (leper is a kind of outcast).
'on return' is a reversal indicator.
'leper' reversed gives 'REPEL'.
(Other definitions for repel that I've seen before include "Nauseate" , "Fill with distaste" , "'Drive back, repulse (5)'" , "Hold off" , "Drive back or ward off" .)