Sex details of French Resistance (6)
I believe the answer is:
gender
'sex' is the definition.
('gender' can be a synonym of 'sex')
'details of french resistance' is the wordplay.
'details' becomes 'gen' (I've seen this in other clues).
'of french' becomes 'de'.
'resistance' becomes 'r' (abbreviation).
'gen'+'de'+'r'='GENDER'
(Other definitions for gender that I've seen before include "Class such as female or male" , "What divides males and females" , "Male or female state" , "Sexual status" , "Man or woman" .)