Father on African Union married woman in Germany (4)
I believe the answer is:
frau
'married woman in germany' is the definition.
(Frau is the German equivalent to 'Mrs')
'father on african union' is the wordplay.
'father' becomes 'fr' (abbreviation as in a priest's title).
'on' means one lot of letters go next to another.
'african union' becomes 'AU' (abbreviation).
'fr'+'au'='FRAU'
(Other definitions for frau that I've seen before include "German woman's title" , "half of Hockenheimring?" , "Foreign woman" , "German title for a woman" , "German partner" .)