- any composite plant of the genus Dahlia, native to Mexico and Central America and widely cultivated for its showy, variously colored flower heads.
- the flower or tuberous root of a dahlia.
- a pale violet or amethyst color.
- of the color dahlia.
- any herbaceous perennial plant of the Mexican genus Dahlia, having showy flowers and tuberous roots, esp any horticultural variety derived from D. pinnata : family Asteraceae (composites)
- the flower or root of any of these plants
1804, named 1791 by Spanish botanist Antonio José Cavanilles for Anders Dahl (1751-1789), Swedish botanist and pupil of Linnaeus, who discovered it in Mexico in 1788. No blue variety had ever been cultivated, hence blue dahlia, figurative expression for “something impossible or unattainable” (1880).