1. Any of the long, slender, often glossy feathers on the neck of a bird, especially a male fowl.
2. hackles The erectile hairs along the back of the neck of an animal, especially of a dog.
3. A feather, usually from the neck of a chicken, used in trimming a fishing fly.
To trim (an artificial fishing fly) with a hackle.
get (one’s) hackles up
To be extremely insulted or irritated.