"To venture a guess" means to make a guess or estimation, usually in a situation where one is uncertain or lacks enough information. It suggests taking a risk in providing an answer without being completely sure of its accuracy.
Sentences with «to venture a guess»
Based on my firm administrator days I can venture a guess at the specifics. (slaw.ca)
I wouldn't venture a guess as to the value of the market. (thebookseller.com)
But would you care to venture a guess how many people drink more coffee than they think is good for them? (planet3.org)