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