The German coming in brought to naught? That's rare (9)
I believe the answer is:
underdone
'rare' is the definition.
(synonyms)
'the german coming in brought to naught?' is the wordplay.
'the german' becomes 'der' ('the' in German).
'coming in' indicates putting letters inside.
'brought to naught?' becomes 'undone' (I've seen this in another clue).
'der' placed into 'undone' is 'UNDERDONE'.
'that's' acts as a link.
(Other definitions for underdone that I've seen before include "Not sufficiently cooked" , "Not cooked enough" , "Insufficiently cooked" , "Inadequately cooked" , "could be rare" .)