an extraordinary or unusual thing, person, or event; an exceptional example or instance.
a printed punctuation mark (‽), available only in some typefaces, designed to combine the question mark (?) and the exclamation point (!), indicating a mixture of query and interjection, as after a rhetorical question.
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)
2.
the flower or root of any of these plants
[C19: named after Anders Dahl, 18th-century Swedish botanist; see -ia]
1804, named 1791 for Anders Dahl (1751-1789), Swedish botanist who discovered it in Mexico. No blue variety had ever been cultivated, hence "blue dahlia," fig. for "something impossible or unattainable" (1880).