1. Any of various plants of the genus Aster in the composite family, having radiate flower heads with white, pink, or violet rays and a usually yellow disk.
2. The China aster.
3. Biology. A star-shaped structure formed in the cytoplasm of a cell and having raylike fibers that surround the centrosome during mitosis.

[Latin astēr, a type of plant, from Greek, star, type of daisy.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.