a plant, Zephyranthes atamasco, of the amaryllis family, of the southeastern U.S., bearing a single white lilylike flower sometimes tinged with purple.
at·a·mas·co lily (āt'ə-mās'kō) n. A bulbous plant (Zephyranthes atamasco) of the southeast United States, having a showy, solitary, white to pinkish flower on a long stalk.