A physician who cares for other doctors' patients overnight.
To bridge the chasm between the day and night shifts, hospitals from Syracuse to Seattle are hiring a new breed of subspecialist called a "nocturnist" — an experienced doctor who works overnight taking care of patients outside the emergency room.
—Sandra G. Boodman, "Shifting the risks at night," The Washington Post, June 7, 2011
Last week I received a mailing from Crouse Hospital where I learned about a new type of doctor I had never heard of before — a nocturnist. ...
Dr. Ronald Greenberg's day is just beginning. Greenberg, one of two new nocturnist physicians at St. Joe's, admits and cares for patients overnight so their regular doctors won't have to get out of bed and come in.
—James T. Mulder, "Hospital allows doctors to get Z's," The Post-Standard, November 8, 2004
A nocturnist can also refer to a composer who writes nocturnes (musical pieces suggestive of night [c. 1829]), or to an artist who paints nocturnes (paintings of night scenes [c. 1872]). The former dates to about 1992, while the latter goes back to at least 1885.