Dog marks a dead body (7)
I believe the answer is:
mastiff
'dog' is the definition.
(mastiff is a kind of dog)
'marks a dead body' is the wordplay.
'marks' becomes 'M' (former German currency).
'dead body' becomes 'stiff' (stiff can informally mean a dead body).
'm'+'a'+'stiff'='MASTIFF'
(Other definitions for mastiff that I've seen before include "Strong breed of dog" , "one of his best friends?" , "Powerful, smooth-coated dog used for security work" , "Big dog" , "Large, powerful, short-haired dog" .)