playmate
A friend your age you often play with.
A playmate is someone, usually around your own age, who you play with regularly. Your playmate might be the kid next door who joins you for backyard soccer games, or your best friend who comes over after school to build elaborate Lego cities with you. The word suggests a comfortable, ongoing friendship built around having fun together.
The term is most commonly used for young children. A five-year-old's playmate might be someone they meet at the playground every Saturday, while a ten-year-old might use the word to describe a younger sibling or cousin they enjoy spending time with. As kids get older, they usually switch to words like “friend” or “buddy” instead.
Parents sometimes arrange playdates so their children can spend time with potential playmates, hoping the kids will hit it off and want to play together again. A good playmate shares your interests, plays fairly, and makes ordinary activities more enjoyable. Whether you're inventing imaginary worlds, playing games, or just goofing around, a playmate turns solo activities into shared adventures.