Englishmen seen with duke? Correct! (5)
I believe the answer is:
emend
'correct' is the definition.
(to emend something is to correct or improve it)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for emend that I've seen before include "get rid of faults" , "Alter something written to correct errors" , "Correct/revise (a text)" , "Correct; edit" , "Polish" .)