from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Nonsense; foolishness.
- interj. Used to express disagreement or exasperation.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- interj. Indicates disbelief.
- n. Nonsense; indicates disbelief.
- n. Long hair on lower legs of a draft horse (e.g., Clydesdale), especially the rear legs.
- n. Feathering strips.
Alteration of horseshit.(American Heritage® Dictionary of the English Language, Fourth Edition)
The "nonsense" sense is horse + feathers, a nonexistent item, as only birds have feathers. Compare hen’s teeth. (Wiktionary)