Judge of French space (4)
I believe the answer is:
deem
'judge' is the definition.
(I've seen this in another clue)
'of french space' is the wordplay.
'of french' becomes 'de' ('of' in French).
'space' becomes 'em' (in typography, a space as wide as a letter 'm').
'de'+'em'='DEEM'
(Other definitions for deem that I've seen before include "Believe" , "Judge, think, consider" , "Regard, consider" , "Card-table felt" , "View as" .)