Apt closure ruined one taking financial risk (10)
I believe the answer is:
speculator
'one taking financial risk' is the definition.
(term for an investor)
'apt closure ruined' is the wordplay.
'ruined' indicates an anagram.
'apt'+'closure'='aptclosure'
'aptclosure' anagrammed gives 'SPECULATOR'.
(Other definitions for speculator that I've seen before include "One gambling on the stock exchange" , "better" , "Stock market gambler" , "Investor in stocks, etc" .)