Criminal in casino pockets million, but he can't get off (9)
I believe the answer is:
insomniac
'he can't get off' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'criminal in casino pockets million' is the wordplay.
'criminal' indicates an anagram.
'pockets' is an insertion indicator.
'million' becomes 'm' (abbreviation).
'in'+'casino'='incasino'
'incasino' anagrammed gives 'insoniac'.
'insoniac' going around 'm' is 'INSOMNIAC'.
'but' acts as a link.
Can you help me to learn more?
(Other definitions for insomniac that I've seen before include "who won't get off?" , "Habitually sleepless person" , "One unable to sleep" , "One who can't sleep" , "Person finding it difficult to sleep" .)