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Wiktionary
hair spray

n. A usually scented hairstyling product in aerosol form that stiffens the hair, so it stays in a certain hairstyle.

WordNet
hair spray

n. toiletry consisting of a commercial preparation that is sprayed on the hair to hold it in place

Wikipedia
Hair spray

Hair spray (also hair lacquer or spritz) is a common cosmetic product that is sprayed onto hair to keep it stiff or in a certain style. The spray can be dispensed from a pump or aerosol spray nozzle.

Modern hair sprays were developed around the time of the aerosol can in the 1940s, and the first patents describing copolymers for hair styling were published in the 1940s.