Definitions:
done or operating in an impressively smooth and efficient way

(of skin or hair) smooth and glossy

an oil slick

an application or amount of a glossy or oily substance

a racing-car or bicycle tyre without a tread, for use in dry weather conditions

a glossy magazine

a person who is smooth and persuasive but untrustworthy.

make (one's hair) flat, smooth, and glossy by applying water, oil, or gel to it