Slip removing cases from ferry port (5)
I believe the answer is:
error
'port' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'slip removing cases from ferry' is the wordplay.
'slip' becomes 'err' (to err is to make an error).
'removing cases from' indicates the central letters (the letters that encase the word are removed).
'ferry' becomes 'ro-ro' (short for roll-on/roll-off).
The central letters of 'roro' are 'or'.
'err'+'or'='ERROR'
Can you help me to learn more?
(Other definitions for error that I've seen before include "Miscalculation" , "Slip-up" , "Mistake or fault" , "Miscarriage of justice" , "wrong" .)