Costly article secured by the German (4)
I believe the answer is:
dear
'costly' is the definition.
(synonyms)
'article secured by the german' is the wordplay.
'article' becomes 'a' (the indefinite article in English).
'secured by' indicates putting letters inside (inserted letters are held or secured).
'the german' becomes 'der' ('the' in German).
'a' inserted within 'der' is 'DEAR'.
(Other definitions for dear that I've seen before include "Overpriced" , "pet > ducks" , "Beloved or costly" , "polite form of address" , "It's not cheap" .)