To rub means to press against something and move back and forth, creating friction. When your hands are cold, you rub them together quickly to warm them up. When you erase a pencil mark, you're rubbing the eraser against the paper. A cat might rub against your leg as a sign of affection.

As a noun, a rub can also mean a difficulty or problem, especially in the phrase the rub. When someone says “there's the rub,” they're pointing out a catch or complication. You might plan a perfect camping trip, but the rub is that it's supposed to rain all weekend.

Rub appears in several common expressions. When something rubs you the wrong way, it annoys or bothers you, like petting a cat backward against its fur. To rub salt in the wound means to make a bad situation worse by saying something hurtful. And when you rub shoulders with someone, you spend time with them, usually someone important or interesting.