"Midnighter" is a term used to refer to someone who is often awake or active during the late-night hours. However, there are many other words and phrases that can be used as synonyms. For instance, "night owl," "insomniac," "nocturnal," "night crawler" and "night hawk" are all similar terms that describe a person who is active during the night. Other words such as "night shift worker," "graveyard worker" and "night watchman" are also used to describe someone who is active during the night hours. These words can be used interchangeably, depending on the context and the writer's preference.