9 Grammatical Pitfalls
"acne pimple," 1966, originally U.S. teenager slang, of unknown origin.
[1966+ Teenagers; origin unknown; perhaps echoic of the squishy pop made when the pus is squeezed from a blackhead]
To set something on fire; ignite something
[1970s+ Army; fr Zippo, trademark of a cigarette lighter, probably fr the sound made as one turns the sparking wheel, and the speed with which the lighter ignites]