Hacky Sack[hăkˈē săkˌ]
The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A trademark used for a footbag. This trademark often occurs in print hyphenated or in uppercase or lowercase as a name for the game of footbag.