Nag when sick, and not even over the hill! (5)
I believe the answer is:
scold
'nag' is the definition.
(I know that nag can be written as scold)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for scold that I've seen before include "Chide, rebuke" , "Castigate" , "Chide - nag" , "Censure, berate" , "Rebuke; nagging woman" .)