shiner
A dark, swollen bruise around the eye after a hit.
A shiner is a black eye: a dark bruise around the eye that turns purple, blue, or greenish-yellow after someone gets hit or bumped hard in the face. The area swells up and changes colors over several days as it heals, creating a distinctive mark that's hard to hide.
Kids might get shiners from accidents during sports, from running into something, or from roughhousing that got too rough. A baseball player might end up with a shiner after a ball takes a bad hop and catches them in the face. Someone learning to skateboard might fall and hit their face on the pavement.
The bruise is called a shiner because the swollen, discolored skin can look shiny under certain light. People used to joke about “sporting a shiner” as if wearing one were a badge of honor, though actually having one is usually painful and embarrassing.
The word can also refer to any small fish with shiny, metallic scales, especially minnows used as bait for fishing. But when someone says they've got a shiner, they almost always mean the bruise, not the fish.