Longing of French father (6)
I believe the answer is:
desire
'longing' is the definition.
(I've seen this in another clue)
'of french father' is the wordplay.
'of french' becomes 'de' ('of' in French).
'father' becomes 'sire' (synonyms).
'de'+'sire'='DESIRE'
(Other definitions for desire that I've seen before include "Want to reside?" , "Crave" , "Strong wish" , "Hanker after" , "Strong need" .)