I was recently exposed to the word horripilation, meaning "a bristling of the hair on the skin from cold, fear, etc." The -pil-, I assumed meant "hair", as in depilation ("removal of hair"), and indeed the Latin pilus means "hair".
I noticed that the horr- at the beginning of horripilation looked a lot like the horr- in the words horror, horrify, horrible, or horrid. Was there a connection? Yes: it turns out that Latin horrēre means "to bristle with fear"; thus, horri-pil-ation means, "a bristling of the hair".
So we have arrived at a deeper understanding of the horr- words: for example, something is horrifying if it causes your hair to stand up ("bristle").