The word "tennis" (probably from the French tenez - to hold or receive - which the server used to shout before serving), had been around for centuries, but in 1874, when Major Walter Clopton Wingfield applied for a patent for his "New and Improved Portable Court for Playing the Ancient Game of Tennis", the name he went for was Sphairistike (from the Greek Sphairos, "ball").
Fortunately, the Old Harrovian chums who helped him test his court dissuaded him. They conducted their research in Lord Lansdowne's garden in Berkeley Square, and the peer's memoirs record that he told Wingfield the name would not work. Arthur Balfour, who had been Lansdowne's fag at Eton and was later Prime Minister, suggested "lawn tennis". A craze was born.
Meanwhile, Major Harry Gem and his friend J B Perera were developing the game they had called pelota, then "lawn rackets". In 1872, they formed the Leamington Lawn Tennis Club, later publishing the Rules of Tennis.