Meaning of hacky-sack in English:

hacky-sack

Pronunciation /ˈhakɪsak/

noun

(also hackie-sack)
US
  • A trademark for: a type of small, round footbag designed to be kicked in the air; (also) any of various games played with such a footbag, in which two or more players pass the bag using legs and feet, without allowing it to touch the ground.

Origin

1970s; earliest use found in Walla Walla Union-Bulletin. From hacky + sack, apparently as an alteration of hack the sack, a name for the game.