Michaelmas daisy

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several asters that have leafy stems and flower in the fall, especially the New York aster.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Aster amellus, a flowering plant.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun North American perennial herb having small autumn-blooming purple or pink or white flowers; widely naturalized in Europe