* Singular: The practice of medicine is challenging.
* Plural: The doctor's practices are located in three different cities.
However, depending on the context, you might use other related nouns:
* Rehearsal: If you are talking about practicing a performance.
* Exercise: If you are talking about practicing a skill or technique.
* Training: If you are talking about a structured program of practice.
* Drill: If you are talking about repetitive practice of a specific action.