Cosmetic refers to how something or someone looks. Visit the cosmetics department of a store if you are looking to buy lipstick, and visit a cosmetic surgeon if you are looking to buy new lips.
The word cosmetic has to do with beauty and appearance. Cosmetic surgery makes someone look better, but isn't necessary medically, like heart surgery. A cosmetic change to a building only changes the building’s appearance. Cosmetic often means the same as decorative or ornamental. Also, cosmetics are items used to adorn, especially women, such as nail polish, lipstick, and eyeliner. All uses of cosmetic have to do with what's on the outside, not what's on the inside.