Discharge lieutenant for dope (4)
I believe the answer is:
dolt
'dope' is the definition.
(thesaurus)
'discharge lieutenant' is the wordplay.
'discharge' becomes 'do'.
'lieutenant' becomes 'lt'.
'do'+'lt'='DOLT'
'for' acts as a link.
(Other definitions for dolt that I've seen before include "dope" , "Dull or stupid fellow" , "Simpleton" , "Halfwit" , "Slow-witted person" .)