Noun

1. One of the peculiar, long, narrow feathers on the neck of fowls, most noticeable on the cock.
2. A feather plume on some soldier's uniforms, especially the hat or helmet.
3. The hair on the nape of the neck.

   When the dog got angry his hackles rose and he growled.

4. A plate with rows of pointed needles used to blend or straighten hair for the purpose of wig making.

Adjective

1. Descriptive of the feathers of a fowl.

   The hackle feathers of the cock were long and golden.