Corrosion observed on Irish ship by last inspector is criminal (7)
I believe the answer is:
rustler
'criminal' is the definition.
(rustler is a kind of criminal)
'corrosion observed on irish ship by last inspector' is the wordplay.
'corrosion' becomes 'rust' (rust is a kind of corrosion).
'observed on irish ship' becomes 'le' (I can't explain this - if you can you should believe this answer much more).
'by' means one lot of letters go next to another.
'last' says to take the final letters.
The last letter of 'inspector' is 'r'.
'rust'+'le'+'r'='RUSTLER'
'is' is the link.
Can you help me to learn more?
(Other definitions for rustler that I've seen before include "Cattle-thief" , "person taking stock" , "Horse thief" , "Livestock thief" , "Stock taker?" .)