Horrid things are absolutely dreadful — they horrify or disgust you. A horrid dream can make you wake with a gasp and lie there with your heart pounding.
You might cover your eyes during a particularly horrid scene in a scary movie, or skip past the horrid photos of a war zone in the newspaper. Things are also horrid when they're just plain bad: "That wallpaper in your bedroom is absolutely horrid." In the 1400s, horrid meant "hairy, shaggy, or bristling." The word stems from a Latin root, horrere, "to bristle with fear."