English musketeer lacks a moral code (5)
I believe the answer is:
ethos
'moral code' is the definition.
(I've seen this in another clue)
'english musketeer lacks a' is the wordplay.
'english' becomes 'e' (abbreviation).
'musketeer' becomes 'athos' (I've seen this before).
'lacks' is a deletion indicator.
'athos' with 'a' taken away is 'thos'.
'e'+'thos'='ETHOS'
(Other definitions for ethos that I've seen before include "Group's distinctive character" , "Distinctive spirit of an institution" , "Those (anag.)" , "Moral atmosphere" , "Underlying culture of a group" .)