In searching for some śaśa-viṣāṇa (horns of the hare) clip art in the form of a jackalope, I discovered this article on Wired.com explaining the origin of the "hare's horn" myth in the US. The idea of a rabbit with horns is not only found in Indian literature (as an example of an impossibility), but also in the American West and in Arabic poetry (known as al-mi'raj). Apparently there is a viral infection that causes some unfortunate rabbits to sprout growths that look like horns, though they don't look as nice as the ones below. (You can Google for images on your own!) So, perhaps it's not an non-referring term after all?