- Pertaining to the hours of darkness; opposite of diurnal (1). [L. nocturnus, of the night]
* * *noc·tur·nal näk-'tərn-əl adj1) of, relating to, or occurring at night <\nocturnal myoclonus>2) characterized by nocturnal activity <a \nocturnal form of filariasis>
* * *noc·tur·nal (nok-turґnəl) [L. nocturnus] pertaining to, occurring at, or active at night.
Medical dictionary. 2011.