Pavonine means being similar to a peacock, like your sister's wonderfully iridescent pavonine Halloween costume.
This adjective can describe anything that reminds you of the large, colorful, showy birds: "My friend put on a pavonine display at school today, strutting around in his fancy new outfit." It's most often used for things that resemble a peacock's brilliant, lustrous feathers, though, like the pavonine feathers of a smaller, less impressive bird. The Latin pavo, "peacock," is the root of pavonine.