Not so many sheep in France (5)
I believe the answer is:
fewer
'not so many' is the definition.
('few' can be the opposite of 'many' so perhaps 'fewer' is reasonable for 'not so many')
'sheep in france' is the wordplay.
'sheep' becomes 'ewe' (I've seen this before).
'in' indicates putting letters inside.
'france' becomes 'fr'.
'ewe' placed within 'fr' is 'FEWER'.
(Other definitions for fewer that I've seen before include "smaller number of people" , "Not so many" , "Reduced" , "in smaller numbers" , "Less in number" .)