Final answer:
Etiology refers to the study of the causes of diseases and, in the context of an epidemic, it identifies the causative agent of the disease.
Step-by-step explanation:
Etiology is a term used in medicine and epidemiology to refer to the study of the causes or origins of diseases. When epidemiologists investigate an epidemic, their initial step is to determine the etiology of the disease, identifying the causative agent or etiological agent. It is crucial to differentiate whether the relationship between a disease and a pathogen is a direct causation or merely an association.
This differentiation often necessitates controlled experiments to rule out other possible causes and confirm the exact cause. The challenge is amplified when the disease signs are nonspecific, and a broad range of pathogens could cause similar symptoms, making the precise identification of the causative agent difficult. Given this context, etiology aligns with the word 'cause' from the provided options.
Etiology is another word for a) cause, as it pertains to the origin or reason behind a disease or condition.