on·cid·i·um \änˈsidēəm\noun Etymology: New Latin, from onc- + -idium; from the shape of the labellum 1.capitalized: a genus of showy tropical American epiphytic or terrestrial orchids with the column short and winged and the labellum usually at right angles to it 2.-s: any plant of the genus Oncidium — called also butterfly plant