A commercial undertaking that's risky, perhaps (12)
I believe the answer is:
peradventure
'perhaps' is the definition.
(synonyms)
'a commercial undertaking that's risky' is the wordplay.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'commercial' becomes 'ad' (abbreviation for advertisement).
'undertaking that's risky' becomes 'venture' (venture can mean a risky undertaking or journey).
'per'+'ad'+'venture'='PERADVENTURE'
(Other definitions for peradventure that I've seen before include "Maybe" , "by chance" , "perhaps" , "Possibly (archaic)" .)