The court noted, however, that according to Urban Dictionary, “jack” means “to steal, or take from an unsuspecting person or store.” It then rejected the convicted man’s claim that he should not have to make restitution to the owner of a van he stole to use in a robbery.

Two weeks earlier, a court in Tennessee noted that a phrase used by a manager at a supply chain logistics company — “to nut” — was defined by Urban Dictionary as “to ejaculate.” After weighing that and other evidence, it rejected a motion to dismiss a sexual harassment claim by female employees.

It can take years for slang terms to be included in traditional dictionaries, whose editors want to be certain that the words have staying power. By contrast, some new words rush into Urban Dictionary in less than a day. As a result, the site has cropped up in dozens of court cases in recent years, according to a Lexis database of federal and state cases, although the outcome rarely rests solely on a definition.

This trend is likely to accelerate, according to Greg Lastowka, a professor of law at Rutgers specializing in Internet and property law. “If it is Urban Dictionary or hire some linguistic expert to do a survey, it seems like a pretty cheap, pretty good alternative for the court,” he said.

In the last year alone, the Web site was used by courts to define iron (“handgun”); catfishing (“the phenomenon of Internet predators that fabricate online identities”); dap (“the knocking of fists together as a greeting, or form of respect”); and grenade (“the solitary ugly girl always found with a group of hotties”).