Final answer:
The term for something done in the same voice, or without variety, is 'monotonously'. It describes a lack of variation in tone or delivery.
Step-by-step explanation:
The term that describes something done in the same voice, or without variety is monotonously. This term is often used to describe a manner of speaking or doing something in one unchanging tone, therefore lacking in variation and interest. While other options like monotheism refer to the belief in one god, and monolithic refers to something large, indivisible, or massive, neither of these terms is related to voice or variety.