It could mean going back over old ground (8)
I believe the answer is:
reversal
'it could mean going back' is the definition.
The definition suggests a singular noun which matches the answer.
'over old ground' is the wordplay.
'over' becomes 're'.
'old ground' becomes 'versal' (I can't justify this - if you can you should believe this answer much more).
're'+'versal'='REVERSAL'
Can you help me to learn more?
(Other definitions for reversal that I've seen before include "A change to an opposite direction" , "misfortune!" , "Turnabout" , "Volte-face" , "About-turn" .)