Craic. It's a word, but it won't appear in Merriam-Webster's dictionary. In fact, it won't appear in many dictionaries, save one: Urban Dictionary.

While it may sound slightly suspect to pass off a word found on a socially created Internet dictionary, know that it has legal precedent in the U.S. justice system. That's right: Urban Dictionary is used as a point of reference, and a source of definition, in court cases throughout the states.

That's according to a report by The New York Times, which found that traditional dictionaries which would've been used in courts to define terms have failed to keep up with the ever-expanding English language and its various slang words.

So now, when a suspect breaks out the word "iron," or "dap," or "shibby" in the courtroom, lawyers are only an Internet search away from understanding what their clients are saying (which are handgun, pounding fists, and expressing approval, respectively).

For example, The Times reports that a financial restitution case in Wisconsin required the use of the social-engineered dictionary to define the term "jack," as in "jack boys." The court found the term to mean "to steal, or take from an unsuspecting person or store."

Another case, this time in Tennessee, required a court to look up the term "to nut," in a sexual harassment case. For the slang averse, the term means to ejaculate and was used by a supply chain logistics manager. The court rejected the manager's motion to dismiss the case.

It's also often a cheaper option as well. Rutgers law professor Greg Lastowka told The Times that courts will likely defer to Urban Dictionary if the other option is hiring a linguistic expert to do a survey.

But not all lawyers approve of using Urban Dictionary to nail down words.

"Using them in court is a terrible idea; they don't claim to be an authority or a reference," Tom Dalzell, senior editor of The New Partridge Dictionary of Slang and Unconventional English said. "Some of the stuff on their site is very good, but there is more chaff than wheat. It is a lazy person's resource."

Which brings us back to the word "craic." Craic, according to Urban Dictionary, is Irish in origin, and means something the legal system has all the time with the English language, and that's to have a good time.