early 15c., "a bauble, trinket," earlier "a large, ornamental bead in a rosary" (mid-14c.), probably mistakenly taken as singular of earlier gaudy (n.) "large, ornamental rosary bead" (early 14c., in plural form gaudeez), later "ornamentation" generally (late 14c.), which is from Medieval Latin gaudia and Old French gaudie "joy, pleasure, playfulness; a piece of showy finery, a flashy trinket," from Latin gaudium "joy," gaude "rejoice thou" (in hymns), from gaudere "rejoice" (see joy (n.), and compare jewel (n.)).
Also in Middle English "a jest, prank, trick" (late 14c.); "a deception, fraud, artifice" (mid-14c.). As a verb, "to furnish with gauds," from late 14c. Related: Gauded; gauding; gaudful; gaudless.