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