A snake moves by curving and winding along the ground. Roads through the Pyrenees, the mountains that separate Spain from France, tend to be serpentine, curving back and forth on themselves up and down the steep slopes. Serpentine has other meanings as well. As a noun, it's the name for a soft green mineral, and also for the party streamers you might throw at midnight on New Year's Eve. The serpentine belt under the hood in your car is the long, looping belt that most of the car's accessories—the AC, the power steering, the alternator, and so on—depend on to get their power.