nocturnal UK /nɒkˈtɜː.nəl/US /nɑkˈtɝ.nəl/adjective 2noun 2forms 3 adjective2 •Of a person, creature, group, or species, primarily active during the night.nocturnal birds •Of an occurrence, taking place at night, nightly. noun2 •A person or creature that is active at night. •(historical) A device for telling the time at night, rather like a sundial but read according to the stars. formsnocturnals · more nocturnal · most nocturnal