What is an abstract noun for sick?

There isn't a single perfect abstract noun for "sick." It depends on what aspect of being sick you want to emphasize. Here are some possibilities:

* Illness: This is the most general and common abstract noun for being sick.

* Sickness: Similar to "illness," but often implying a more severe or prolonged state.

* Ailment: Refers to a specific illness or health problem.

* Malaise: A general feeling of discomfort, uneasiness, or illness.

* Disease: A specific condition with identifiable symptoms and causes.

* Infection: A state of being infected by a pathogen.

* Debilitation: A state of weakness and loss of strength.

The best choice will depend on the specific context of your writing.