Empty dyke covered in corrosion is most offensive (6)
I believe the answer is:
rudest
'most offensive' is the definition.
(I've seen this in another clue)
'empty dyke covered in corrosion' is the wordplay.
'empty' says to hollow out the word (remove centre letters).
'covered in' means one lot of letters goes inside another.
'corrosion' becomes 'rust' (rust is a kind of corrosion).
'dyke' with its middle taken out is 'de'.
'de' placed inside 'rust' is 'RUDEST'.
'is' is the link.
(Other definitions for rudest that I've seen before include "Most bad mannered!" , "Least polite, most unmannerly" , "Most vulgar" , "Most impolite" , "Most unrefined" .)