Cut a key in crude fashion (6)
I believe the answer is:
reduce
'cut' is the definition.
(synonyms)
'a key in crude fashion' is the wordplay.
'a key' becomes 'e' (I've seen this in other clues).
'in' indicates putting letters inside.
'fashion' indicates an anagram.
'crude' with letters rearranged gives 'rduce'.
'e' put into 'rduce' is 'REDUCE'.
(Other definitions for reduce that I've seen before include "Lower" , "Make or become smaller" , "Subjugate; make (sauce) thicker" , "Make smaller or slim down" , "Make smaller or lose weight" .)