Definition of "ragweed" [rag•weed]

• Any of various weeds of the genus Ambrosia having small, greenish, unisexual flower heads and producing abundant pollen that is one of the chief causes of hay fever. (noun)
• Chiefly British Ragwort. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "If you're allergic to other plants, such as ragweed, your risk of an allergic reaction to Calendula may be greater."
• "Old field plant communities are composed primarily of successional species such as ragweed, asters, goldenrod, sumac, wild carrot and various grasses."
• "Cetirizine Hydrochloride syrup is indicated for the relief of symptoms associated with seasonal allergic rhinitis due to allergens such as ragweed, grass and tree pollens in adults and children 2 years of age and older."