Bats are nocturnal. They hunt at night. Deer are crepuscular. They are active at dawn and dusk. Cheetahs are diurnal . They hunt during the day.

I searched for the meaning of "crepuscular". No result in Longman was found. However, in the other dictionaries it seems that it means : twilight.
My question is what's the relation among nocturnal, crepuscular and diurnal. I didn't find anywhere such a combination : crepuscular animals!