spectral

This word has a split personality, which is exactly the kind of thing etymology likes to pull on you. In 1718, English had a fresh adjective for anything ghostly and half-seen: spectral, built from spectre plus the neat little adjective ending -al. But the story doesn’t stop in a haunted hallway; by 1832, the same shape was being used for the rainbow-sliced business of a spectrum, as if the word had wandered from a graveyard into a physics lab. That makes it cousins with inspect, suspect, spectacle, and perspective — all of them descendants of Latin specere, “to look,” which is a wonderfully ordinary root for such an eerie word. So spectral ends up meaning both “of ghosts” and “of bands of light,” which is a pretty good reminder that English loves a word that can stare back at you and split the room in two.