A more thorough explanation:

Definition: A concubitor is a person who keeps a concubine.

Example: In ancient Rome, wealthy men often had concubitors who would keep their concubines for them.

Explanation: A concubitor is someone who is responsible for taking care of a concubine, which is a woman who is not a man's wife but is kept by him for sexual purposes. The example illustrates how in ancient Rome, men who were wealthy enough to have concubines would often hire concubitors to take care of them.