Some French revolutionary had to calm down (6)
I believe the answer is:
sedate
'to calm down' is the definition.
(sedate can mean to calm or relax)
'some french revolutionary had' is the wordplay.
'some french' becomes 'des' ('some' in French).
'revolutionary' says the letters should be written backwards.
'had' becomes 'ate' (e.g. I had an ice cream).
'des' in reverse letter order is 'sed'.
'sed'+'ate'='SEDATE'
(Other definitions for sedate that I've seen before include "boring" , "Calm and demure" , "Calm or spectral appartition" , "Dignified - staid" , "Staid; put to sleep" .)