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