Having more of these, you must want more (5)
I believe the answer is:
needs
'having more of these you must' is the definition.
The definition suggests an adverb but the answer is an adverb.
'want more' is the wordplay.
'want' becomes 'need' (needing is a kind of wanting).
'more' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'need'+'s'='NEEDS'
Can you help me to learn more?
(Other definitions for needs that I've seen before include "Wants, requires" , "What is required" , "Requires or lacks" , "Calls for" , "What we require" .)