The antonyms for the word "most crepuscular" are "least nocturnal" or "most diurnal." While crepuscular animals are most active during the dawn and dusk hours, nocturnal animals are active during the night, and diurnal animals are active during the day. Thus, using the term "least nocturnal" would describe animals that are not active during the night but during the day, such as birds and squirrels. On the other hand, "most diurnal" would describe animals that are mainly active during daylight hours, such as lions, zebras, and monkeys. By using these antonyms, one can convey the opposite meaning of "most crepuscular" in a concise yet effective manner.