How can you tell that something is repellent? You dislike it so much, you want nothing to do with it. If something is repellent, it is highly offensive or disgusting.
To correctly pronounce repellent, accent the second syllable: "ruh-PELL-unt." Being repellent is sometimes a good thing, like when you're camping — your water-repellent tent gets you through a rainstorm and bug repellent keeps you free of itchy bites. The word originates from the Old French word repeller, meaning "to drive away, remove."