An ancient more primitive love affair (5)
I believe the answer is:
amour
'love affair' is the definition.
(I've seen this in another clue)
'an ancient more primitive' is the wordplay.
'an' becomes 'a'.
'ancient more' becomes 'mo' (I can't explain this - if you can you should give a lot more credence to this answer).
'primitive' becomes 'ur' (prefix meaning the earliest or original).
'a'+'mo'+'ur'='AMOUR'
Can you help me to learn more?
(Other definitions for amour that I've seen before include "Sexual liaison" , "beloved" , "Result of Cupid's darts" , "(Secret) lover" , "Romantic liaison" .)