Revolutionary left with a smack on the buttocks (5)
I believe the answer is:
natal
'the buttocks' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'revolutionary left with a smack on' is the wordplay.
'revolutionary' is a reversal indicator.
'left' becomes 'l' (common abbreviation).
'with' says to put letters next to each other.
'smack on' becomes 'tan' (I can't explain this - if you can you should believe this answer much more).
'l'+'a'+'tan'='latan'
'latan' written backwards gives 'NATAL'.
Can you help me to learn more?
(Other definitions for natal that I've seen before include "Of or from one's birth - in S African province" , "dealing with delivery" , "old province" , "Concerned with the birth" , "African area" .)