noun · an adhesive substance used to join objects together; the act of sticking with adhesive

他用胶把破损的信封粘好了。

noun · an elastic material, either natural or synthetic, used for tires and other products

这种球是用高弹性的胶制成的，回弹很快。

noun · a viscous, sticky substance secreted by plants; resin

树干上流出了透明的树胶。