Risky undertaking (7)
I believe the answer is:
'risky undertaking' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for venture that I've seen before include "Dare, take a chance" , "Undertake a risky course of action" , "Commercial undertaking that risks a loss but promises a profit" , "Undertaking that involves risk" , "Uncertain undertaking" .)