snow-in-summer

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

• noun A mat-forming perennial herb (Cerastium tomentosum) native to Europe and widely cultivated for its silvery leaves and white flowers.

from The Century Dictionary.

• noun A garden name of Cerastium tomentosum. See snow-in-harvest.

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

• noun chickweed with hairy silver-grey leaves and rather large white flowers
• noun annual spurge of western United States having showy white-bracted flower clusters and very poisonous milk