1620s, from French feston (16c.), from Italian festone, literally "a festive ornament," apparently from festa "celebration, feast," from Vulgar Latin *festa (see feast (n.)). The verb is attested from 1789. Related: Festooned.
festoon fes·toon (fě-stōōn')
A carving in the base material of a denture that simulates the contours of the natural tissue being replaced by the denture.