Crossword Genius

Having more of these, you must want more (5)

Ross

I believe the answer is:

needs

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'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" .)

I've seen this clue in The Telegraph.
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