Real Dictionary

four-o'clock in British English
any of a genus (Mirabilis) of chiefly tropical American plants of the four-o'clock family, bearing petal-less flowers and, often, brightly colored leaves; esp., a garden plant (M. jalapa) with long-tubed blossoms that generally open at about 4:00 p.m.
designating a family (Nyctaginaceae, order Caryophyllales) of dicotyledonous plants, including the bougainvilleas
noun: a common garden plant, Mirabilis jalapa, of the four-o'clock family, having tubular red, white, yellow, or variegated flowers that open late in the afternoon
noun: a tropical American nyctaginaceous plant, Mirabilis jalapa, cultivated for its tubular yellow, red, or white flowers that open in late afternoon