Risky enterprise involving one unknown composer (5)
I believe the answer is:
bizet
'composer' is the definition.
(I've seen this before)
'risky enterprise involving one unknown' is the wordplay.
'risky enterprise' becomes 'bet' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'involving' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'unknown' becomes 'z' (algebra).
'i'+'z'='iz'
'bet' placed around 'iz' is 'BIZET'.
Can you help me to learn more?
(Other definitions for bizet that I've seen before include "French composer of 'Carmen'" , "French opera composer, d. 1875" , "Georges __; French composer" , "Composer of the opera Carmen, d. 1875" .)