In September, the French take a rest (5)
I believe the answer is:
sleep
'a rest' is the definition.
('sleep' can be a synonym of 'rest')
'in september the french' is the wordplay.
'in' is an insertion indicator.
'september' becomes 'sep' (short for September).
'the french' becomes 'le' ('the' in French).
'sep' enclosing 'le' is 'SLEEP'.
'take' is the link.
(Other definitions for sleep that I've seen before include "Be dormant" , "Produced (egg)" , "Drop off" , "Slumber" , "Wayne _; former Royal Ballet principal dancer" .)