William's number one raised huge sum (7)
I believe the answer is:
billion
'huge sum' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'william's number one raised' is the wordplay.
'william' becomes 'bill'.
'number' becomes 'no.' (abbreviation for 'number').
'one' becomes 'i' (Roman numeral).
'raised' is a reversal indicator (going up in a down clue).
'no'+'i'='noi'
'noi' written backwards gives 'ion'.
'bill'+'ion'='BILLION'
Can you help me to learn more?
(Other definitions for billion that I've seen before include "One thousand million" , "A large number" , "1,000,000,000" , "One followed by nine zeros" .)