VIP lifted prohibition of humming (5)
I believe the answer is:
nabob
'vip' is the definition.
(I've seen this before)
'lifted prohibition of humming' is the wordplay.
'lifted' shows that the letters should be reversed in order (going up in down clue).
'prohibition' becomes 'ban' (ban is a kind of prohibition).
'of humming' becomes 'ob' (I can't explain this - if you can you should give a lot more credence to this answer).
'ban' written backwards gives 'nab'.
'nab'+'ob'='NABOB'
Can you help me to learn more?
(Other definitions for nabob that I've seen before include "Mogul governor; very rich or important person" , "Person of conspicuous wealth or high status" , "he may be loaded" , "Wealthy and powerful person" , "Devotional painting" .)