of or pertaining to the night ( opposed to diurnal ).

done, occurring, or coming at night

nocturnal visit.

active at night ( opposed to diurnal )

nocturnal animals.

opening by night and closing by day, as certain flowers ( opposed to diurnal ).

Archaic . an astrolabe for telling time at night or for determining latitude by the position of certain stars in reference to Polaris.

adjective

after dark , late , night , night-loving , nightly , nighttimenotes:nocturnal means belonging to or active during the night; diurnal means belonging to or active during the day , nighttime