(Habitus or Hexis).— Broadly speaking, a settled or stable disposition in a thing.  In its strongest sense, a habit (or habitus) is not devoid of awareness or freedom.  

Entitative Habit.— A habit that determines the existence of a thing—as opposed to its operations—in a way that is beneficial or harmful to the thing. E.g., health or sickness. 

Operative Habit.— A habit by which a power is shaped for a specific kind of operation, even when not actually operating.  Because specific kinds of operations are either perfective or defective vis-à-vis a given power, habits are also perfective or defective.  Perfective habits are called virtues, defective habits are called vices. All virtues perfect a given power. Specifically moral virtues perfect an appetite (whether sensitive or intellectual) in such a way that the agent with the virtue is prepared to elicit perfective actions at the necessary times without difficulty.