In prohibition, bank a thousand less (3)
I believe the answer is:
ban
'in prohibition' is the definition.
'ban' can be an answer for 'prohibition' (synonyms). I am not sure about the 'in' bit.
'bank a thousand less' is the wordplay.
'a thousand' becomes 'K' (K can mean thousand, e.g. 10k).
'less' indicates named letters should be taken away (less can mean minus).
'bank' with 'k' taken away is 'BAN'.
Can you help me to learn more?
(Other definitions for ban that I've seen before include "Veto" , "outlaw" , "Stop" , "Embargo" , "Bar, prohibition" .)