When something is frosty, it's very cold or covered with frost (those tiny ice crystals that form on windows and grass on freezing mornings). A frosty winter day makes your breath visible in the air. Frosty grass crunches under your feet before the sun melts the ice away.

The word also describes a cold, unfriendly attitude. When someone gives you a frosty reception, they're not actually frozen, but they're acting distant and unwelcoming. Maybe you forgot your friend's birthday, and now their responses to you feel frosty: short, cold, and lacking their usual warmth. A teacher might give a student a frosty look when they're caught passing notes, a silent warning that needs no words.

This second meaning works because we associate cold temperatures with the absence of warmth, and warmth is how we describe friendly, caring feelings. When relations between two people become frosty, it's like the friendship has frozen over and needs to thaw again. The weather might be frosty, but hopefully your friendships aren't.