A cow moos, a dog barks, a rooster crows, and a horse whinnies. Whinny is both a noun and a verb. As a noun, it's the sound a horse makes. As a verb, it's the horse making the sound.
A familiar word with the same meaning as whinny is neigh. When you visit your cousins on their farm, the rooster wakes you up every morning with his crowing. The cow moos to let you know she’s ready to be milked. The dog’s barking alerts you that the tractor is coming down the drive. And it’s the horse’s whinny that tells you he’s ready to go for a ride. Every time you hear that whinny, you’ve got to saddle up!