In Chicago, politicians were caught on tape discussing the old standbys “lettuce” and “Cheddar.”

Food makes sense as a cover word for money, said Robert A. Leonard, head of the forensic linguistics program at Hofstra University: Both are desirable, and food often sounds natural in regular conversation.

“The best code words are language that seem to mean something totally different than what it really means, but seems to fit into the context,” said Mr. Leonard, who testifies as an expert language witness in criminal cases. “Food is good because it’s quotidian.”

The magic word doesn’t have to be a foodstuff. In a 1995 case, a former New York City transportation official prosaically referred to payoffs as “commitments.” Farther afield, in South Africa, the code phrase was “Eiffel Tower”; in the Democratic Republic of Congo it was “making a whiskey”; and in Lebanon a common remedy for unlined pockets is “aspirin.”

Secret language often figures in perjury and bribery cases, Mr. Leonard said, because these are crimes that are often “committed via the uttering of a word.”