Pucker is a verb for what happens when something smooth or flat gets folded up into little wrinkles, like how you pucker your lips when you go to kiss someone — you, wild flirt, you!
When you use a sewing machine, sometimes the cloth puckers in wrinkly clumps that make it hard to sew in a straight line. Most of the time, it’s lips that do the puckering, maybe because you want a kiss, but also sucking on a lemon can make your lips pucker. If someone tells you to “pucker up,” they might want to kiss you, or they might throw a sour pickle at your head. Either way, get ready.