In medicine, an acute disease is a disease with either or both of:

1. a rapid onset;
2. a short course (as opposed to a chronic course).

This adjective is part of the definition of several diseases and is, therefore, incorporated in their name, for instance, severe acute respiratory syndrome, acute leukemia.

The term 'acute' may often be confused by the general public to mean 'severe'. This however, is a different characteristic.

Acute hospitals are those intended for short-term medical and/or surgical treatment and care.

Subacute means:

1. Between acute and chronic: subacute fever symptoms; subacute endocarditis.