If you live in the U.S., you'll know that the term 'stop and frisk' has been much in the news of late, especially in regard to New York City's policing practices. It's become a conventional enough phrase at this point, so it took me a long time to think about the word "frisk" embedded in it. Frisk as in frisky? Or just what, exactly?
Frisk makes it way into written English in 1510, with the meaning of "to dance or frolic". Middle English had it as "lively", stemming from Middle French frisque, which meant lively or brisk, and in Old French had meant fresh or new, lively or animated. Great. But none of this seems much related to the experience of being stopped by the police and being patted down for weapons or contraband, does it? The Online Etymology Dictionary that frisk in the sense of a patdown is recorded from 1781. It doesn't, however, show us how language made the leap between the two meanings.
Luckily The Word Detective is a bit more informative. (You have to scroll down a bit, but you'll find it.) Frisk, meaning to move briskly, gradually came to include such things as brisk movements of the hands. (Brisk and frisk are apparently unrelated, by the way, much to my surprise.) In fact, because brisk movements of the hand were part of the pickpocket's repertoire of skills, the word was 18th century slang for "a thief". (Also "frisker".)
The interesting part about this is that "frisk" changed sides. From meaning "to dip into someone's pockets to steal something", it switched over to mean to search a person for illicit goods. This is not the only time this has happened. Turns out "cop" has followed a similar trajectory.
Now that I've gotten this far, I see that the Wall Street Journal has beaten me to the punch and written of much the same topic just three days ago. I will say that the writer delved down and found the name of the 1789 book in which "frisk" in this sense first appears in print. But for the answer to that, you are going to have to go HERE.