It’s the Word of the Day at Merriam-Webster, so here is a context clues worksheet on the adjective aghast. It means “struck with terror, amazement, or horror” and “shocked.”
The word derives from the Middle English verb gasten, “to frighten.” As you may perceive, this is also the source of the adjective ghastly. Not surprising, I suppose, since things that are ghastly generally cause us to feel aghast.
If you find typos in this document, I would appreciate a notification. And, as always, if you find this material useful in your practice, I would be grateful to hear what you think of it. I seek your peer review.