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