In Marseille, a perfect spring (4)
I believe the answer is:
leap
'spring' is the definition.
(synonyms)
'in marseille a perfect' is the wordplay.
'in' says the answer is hidden in the clue.
'LEAP' is hidden within 'marseille a perfect'.
(Other definitions for leap that I've seen before include "'Look before you . . . .'" , "Abrupt change; spring" , "Basket" , "as 1984 was" , "Sort of year" .)