What's the plural form of hacky sack? Here's the word you're looking for.
Answer
The noun hacky sack can be countable or uncountable.
In more general, commonly used, contexts, the plural form will also be hacky sack.
However, in more specific contexts, the plural form can also be hacky sacks e.g. in reference to various types of hacky sacks
or a collection of hacky sacks.
