(by extension) A thin, shiny foil used for ornamental purposes, often in the form of narrow glittering strips, traditionally used to decorate christmas trees or other objects, and can also refer to anything superficially shiny and showy.

Adorn something with shiny material, particularly gold or silver thread, or to decorate something in a gaudy and showy manner.

(figurative) To give (something) a false or superficial attractiveness.

(by extension) The adjective "tinsel" represents something that appears beautiful and expensive but lacks value, being superficially attractive, gaudy, showy, and tawdry.