Had regrets about (4)
I believe the answer is:
'had regrets about' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rued that I've seen before include "Bitterly regretted" , "was remorseful" , "Was contrite about" , "Was sorry" , "'Regretted, repented (4)'" .)