A person who walks around at night, often without a specific purpose or destination. The nightwalker strolled through the quiet streets, enjoying the solitude and the cool night air.
A person who sleepwalks, moving around while still asleep. The family was concerned about their son, a nightwalker, who often wandered the house in his sleep.
Slang, chiefly dated: a prostitute who solicits clients on the streets at night. The detective suspected the victim had been a nightwalker working the downtown district.