pucker
To tighten and wrinkle, especially by drawing together tightly.
To pucker means to gather or wrinkle into small folds or creases, usually by drawing together tightly. When you taste something extremely sour, like a lemon or a Warhead candy, your lips naturally pucker as they squeeze and scrunch inward. Your mouth makes that tight, wrinkled shape almost automatically, like it's trying to protect itself from the intense flavor.
Fabric can pucker too. When you sew something and the thread pulls too tight, the cloth bunches up into little wrinkles instead of lying flat and smooth. A shirt might pucker around badly sewn seams, creating those annoying bumps and ridges.
The word captures that specific gathering motion, whether it's your grandmother puckering her lips to give you a kiss on the cheek, or the way your forehead puckers into wrinkles when you're concentrating hard on a difficult problem. A pucker (as a noun) is the wrinkled result of this gathering action, like the pucker around a drawstring bag when you pull the strings tight.