Daysleeper is a term generally used to describe someone who sleeps during the day and stays awake at night. While there are no exact synonyms for this term, there are several other words that can describe a similar situation. "Night owl" is a term used to describe people who stay up late into the night and sleep during the day. "Nocturnal" is used to describe animals that are active at night. "Shift worker" is a term used to describe people who work irregular hours, including night shifts. "Insomniac" is used to describe people who have difficulty sleeping at night and may sleep during the day. Different words can accurately describe different situations.