In last night's presidential debate, Barack Obama said that Mitt Romney's economic plan amounted to a "sketchy deal." Soon thereafter, #SketchyDeal was a trending topic on Twitter (in part thanks to the Obama campaign's own Twitter account), used to question or criticize various aspects of Romney's proposals. With sketchy in the spotlight, it's worth sketching out how the word came to prominence, and how it can mean different things to different people.

Here's how Obama used sketchy:

Governor Romney was a very successful investor. If somebody came to you, governor, with a plan that said, here, I want to spend $7 or $8 trillion, and then we're going to pay for it, but we can't tell you until maybe after the election how we’re going to do it, you wouldn't have taken such a sketchy deal and neither should you, the American people, because the math doesn't add up.

Sketchy has a number of historical meanings that chime well with Obama's usage. The earliest attested definition of the word, according to the Oxford English Dictionary, is "giving only a slight or rough outline of the main features, facts, or circumstances without going into details," which dates back to 1805. A later development was the sense "of a light, flimsy, unsubstantial or imperfect nature," first showing up in 1878. So sketchy could suggest that Romney's economic plan is both insufficiently detailed and flimsy in nature.

But neither of those older definitions quite hits the mark, even if they provide some added texture to the word. In this context, sketchy could also mean "untrustworthy" or "shady," which has been the ascendant meaning of the word over the past couple of decades. Nancy Friedman talked about this newer sense of the word in her Candlepower column last year, "Sketchy Branding." Nancy in turn linked to an earlier discussion by Language Log's Mark Liberman, who pinpointed the rise of the "questionable" meaning of sketchy to the early '90s in student usage. Grant Barrett, in a comment on Language Log, relayed the recollection of a listener to the "Way with Words" public radio show, pegging its origin to crystal meth users in the '80s: someone under the influence of meth (a sketcher) was considered sketchy or dangerously unreliable.

While drug addicts may have had cause to use the new meaning of sketchy in the '80s, I don't think the usage originated with them. As I wrote in an "On Language" column for The New York Times in 2010, sketch and sketchy have had treacherous undertones in student slang going all the way back to the '70s. A list of slang items used by students at the University of Arkansas, Fayetteville, published in 1975, defined sketch as an adjective meaning "dangerous, risky," illustrated with the example, "I think we're in a sketch situation."

This "iffy" meaning of sketch(y) has taken on increasing importance in youth-culture circles in recent years, often to describe unknown individuals who might present a danger (a.k.a. sketchballs). Connie Eble, a University of North Carolina English professor who has her students compile slang lists every semester, told us in a 2008 interview that sketch and sketchy, meaning "potentially dangerous," were the most frequently attested terms in her students' lists. (They've since been usurped by YOLO.)

Obama's use of sketchy, then, is marvelously ambiguous. Older viewers of the debate might have heard it one way: Obama was criticizing Romney for not supplying enough details, rendering his economic plan unsubstantial. Younger viewers, on the other hand, would hear Obama to mean that the "deal" Romney was offering the public was too risky to rely on. (Still others might have been reminded of a Romney adviser's unfortunate "Etch a Sketch" comment earlier this year.) Perhaps in debate prep, the president's handlers were aware of this ambiguity and suggested he use sketchy precisely for its ability to speak to multiple audiences. Or perhaps I'm reading too much into this sketchy situation.

Here's video of Obama's remarks from Slate, which called the sketchy line the "best use of slang" during the debate: