In Paris, you double the skirt (4)
I believe the answer is:
tutu
'skirt' is the definition.
(tutu is a kind of skirt)
'in paris you double the' is the wordplay.
'in' is an insertion indicator.
'paris' becomes 't' (I am not sure about this - if you are sure you should believe this answer much more).
'you' becomes 'u' (I've seen this in other clues).
'double' indicates the doubling of some letters.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'u' duplicated is 'uu'.
't'+'uu'='tuu'
'tuu' placed around 't' is 'TUTU'.
Can you help me to learn more?
(Other definitions for tutu that I've seen before include "A ballerina's short skirt" , "Archbishop Desmond" , "Ballet dancer's short skirt" , "The old primate" , "8 [BALLET] term" .)