Chummy means friendly and familiar, like you've known someone for a long time. When two people are chummy, they act comfortable around each other, sharing jokes, friendly teases, and easy conversation.

You might notice two classmates being chummy after working together on a science project for weeks, now laughing at inside jokes and finishing each other's sentences. Or maybe a new student becomes chummy with your group surprisingly fast, fitting right in as if they'd always been there.

The word has a warm, informal feeling to it. You wouldn't say a principal and a student are chummy (that sounds too casual), but you might say two teammates became chummy during summer camp. Sometimes adults use it with slight suspicion, like when a politician seems overly chummy with people he wants something from.

Related words like pal and buddy capture similar feelings of informal friendship. When you're chummy with someone, you're on friendly, comfortable terms, though maybe not best friends forever. It's that pleasant space where you genuinely enjoy someone's company and feel relaxed around them.