Mycology: the study of fungi
Entomology: the study of insects
Astrology: the study of the positions and movements of celestial bodies and their influence on human affairs
Pathology: the study of diseases and their causes, processes, and effects

The word that is different from the rest is Astrology.

Explanation:
Mycology, Entomology, and Pathology are all scientific fields that focus on the study of specific subjects - fungi, insects, and diseases respectively. They all involve systematic observation, classification, and analysis of their respective subjects.

However, Astrology is different from the rest because it is not considered a scientific field. Astrology is based on the belief that the positions and movements of celestial bodies have an influence on human affairs and personality traits. It is often associated with making predictions and interpretations based on horoscopes, zodiac signs, and birth charts.

While astrology may have cultural and historical significance in some societies, it does not adhere to scientific principles and methods. Scientific fields like mycology, entomology, and pathology are based on empirical evidence, experimentation, and the application of scientific theories.

In summary, mycology, entomology, and pathology are scientific disciplines that focus on the study of specific subjects, whereas astrology is a belief system that is not scientifically validated. Therefore, astrology is the word that is different from the rest.