Crook skimmed banknote (3)
I believe the answer is:
ill
'crook' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'skimmed banknote' is the wordplay.
'skimmed' means to remove the first letter (to skim something is to take the top off it).
'banknote' becomes 'bill' (synonyms).
'bill' with its first letter taken away is 'ILL'.
Can you help me to learn more?
(Other definitions for ill that I've seen before include "Where Chicagoans are briefly" , "Badly - in need of medical care" , "state of America" , "Hardly - sick" , "Green round the gills" .)