Final answer:
The synonym for 'venture' can be 'opportunity,' which denotes a risky or daring undertaking, whereas the antonym could be 'certainty,' referring to a situation not associated with risk or doubt.
Step-by-step explanation:
When seeking an antonym and synonym for the word venture, one can consider various words depending on the context. As a noun or verb, venture often refers to a risky or daring journey or undertaking. A suitable synonym for venture could be opportunity, which also refers to a set of circumstances that makes it possible to do something, often implying a chance to achieve something or take a risk. Conversely, an antonym for venture could be certainty, which reflects a situation that is guaranteed or not subject to any risk or doubt, thereby contrasting the idea of risk inherent in a venture.