Lord Charles Venturi was the head of his household in the court of Lord Winder during the events of Night Watch. He and Lord Selachii cordially detested one another. Or at least, their families traditionally did. He was also much married, all to the same woman. When talking to Lady Roberta Meserole he was acutely aware that his wife's radar 'could fry an egg at fifty paces'.
He is also Colonel-Commander of at least one regiment raised by family money, Lord Venturi's Medium Dragoons, which effectively means problems if the Ankh-Morporkian Army calls for it to work alongside any Regiment raised by Selachii family money and commanded by Lord Selachii. As we effectively see in Night Watch.
Very impressively, on Roundworld, a "Venturi" meter is to do with controlling the flow of jets and "Selachian" means "of sharks". Sharks and Jets. Gettit? The warring factions in West Side Story, based on the Capulets and the Montagues of Romeo and Juliet. Very, very clever indeed.
A venturi is also the exhaust on a recoil-less cannon (such as the 120mm WOMBAT anti-tank system) which allows what would otherwise be the recoil of the weapon to blast itself out as hot air and flame; it is vitally important not to stand immediately behind a WOMBAT system when it is fired. Pink steam may result for the unwary.
Conversely, the main section of the carburettor on an internal combustion engine, where air and fuel are mixed together prior to entering the combustion chamber, is also called a venturi, as it uses the same principle to reduce the vapour pressure of the fuel, thereby vaporising it. (In the automotive and aviation industries, carburettors have mostly been superseded by fuel injection.)
Both are named after Giovanni Battista Venturi (1746-1822), the Italian physicist who first characterised the effect.