Deliver diamonds in German city (4,4)
I believe the answer is:
hand over
'deliver' is the definition.
('hand over' can be a synonym of 'deliver')
'diamonds in german city' is the wordplay.
'diamonds' becomes 'd' (abbreviation in bridge say).
'in' is an insertion indicator.
'german city' becomes 'hanover' (I've seen this before**).
'd' going into 'hanover' is 'HAND OVER'.
(Other definitions for hand over that I've seen before include "Yield possession of in overhand way" , "Pass something to control of another - manually?" , "Pass across; surrender" , "Deliver into control of another - in manual way?" , "Transfer" .)