This Groundhog Day, we are shining some light on the word shadow. You might think shadow and its kin are clearcut: everyone knows what a shadow is, right? (来源：英语学习门户 http://www.EnglishCN.com)

It isn't as easy to describe as you might think. The sort of shadow associated with today names the partial darkness or obscurity within a part of space from which rays from a source of light (the sun) are cut off by an interposed opaque body (the groundhog).

But then there's the shadow that names a reflected image, such as one in the water. Shadow can refer to an imitation or copy of something (a shadow of her older sister), and it can name a phantom or ghost (as in Shakespeare's "horrible shadow"). Shadow can describe a vestigial trace or emaciated or enfeebled version of another—a hearkening back to the past—and it can be used as an obscure indication of the future, or foreshadowing.

Now that we've reviewed some of the various murky meanings attached to shadow, let's delve into the darkness of that word's linguistic history. Appropriately enough, the Old English ancestor of the word that developed into shadow was formed from the oblique case form of the word for shade. We could, of course, explain more about the oblique case than the straightforward fact that it names a grammatical case other than the nominative and the vocative, but we'd prefer to leave you in the dark.