Surname of one of the old noble families in Ankh-Morpork, the most powerful city-state on the Sto Plains. The Venturi family cordially detest the Selachii family, and vice versa. Put another way, the two families hate each other but, as befits noblemen, are extremely polite about it. They do carry on conversations with each other when they happen to meet in parties, and so that they do not embarrass themselves, they only talk of extremely non-controversial subjects. Known past members of the Venturi family include: Lord Charles Venturi, back in the times of Lord Winder and Mad Lord Snapcase. Lady Alice Venturi, the noted lady explorer whose early life was marked by a sheltered and somewhat selective education, comes from an earlier generation still. There was a Lord Venturi during the events of Jingo who formed the regiment Lord Venturi's Heavy Infantry for the war with Klatch. He though it was a fine idea to kit out his men in nice smart red and white uniforms so that they would stand out in the desert.
On a side note, given that "Selachii" is the Latin term used by biologists to refer to the shark family (and a venturi being part of most jet engines), it seems reasonable to postulate that some comparison with Bernstein's two warring teen groups, the Sharks and Jets of West Side Story, is intended in the names of Ankh-Morpork's two rival families. This is further borne out by their comparison, in Wyrd Sisters, with the two antagonist groups in Shakespeare's Romeo and Juliet, the Montagues and Capulets, who of course formed the basis for the idea of the Sharks and Jets.