Frenchman covered by DUP in ditch (4)
I believe the answer is:
dump
'ditch' is the definition.
(I know that ditch can be written as dump)
'frenchman covered by dup' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'covered by' indicates putting letters inside.
'm' going inside 'dup' is 'DUMP'.
'in' acts as a link.
(Other definitions for dump that I've seen before include "Dispose of" , "Offload" , "Disposal site" , "number two" , "deposit" .)