Can a man own a word? And can he sue to keep other people from using it?

Over the last few years, Leo Stoller has written dozens of letters to companies and organizations and individuals stating that he owns the trademark to "stealth." He has threatened to sue people who have used the word without his permission. In some cases, he has offered to drop objections in exchange for thousands of dollars. And in a few of those instances, people or companies have paid up.

"If a trademark owner doesn't go up to the plate each day and police his mark, he will be overrun by third-party infringers," Mr. Stoller, a 59-year-old entrepreneur, said in a telephone interview from his office in Chicago. "We sue a lot of companies."

Mr. Stoller owns and runs a company called Rentamark.com, which offers, among other things, advice on sending cease-and-desist letters and Mr. Stoller's services as an expert witness in trademark trials. Through Rentamark, Mr. Stoller offers licensing agreements for other words he says he owns and controls, such as bootlegger, hoax and chutzpah, and sells t-shirts and other merchandise through what the Web site calls its "stealth mall."

He is currently in a legal dispute with Sony's Columbia Pictures unit over a film that opens late this month. It is about elite Navy pilots and titled -- what else? -- "Stealth."