balloon flowern. A perennial plant (Platycodon grandiflorus) native to East Asia, having large balloon-shaped buds and usually blue star-shaped flowers, and cultivated as an ornamental.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.