Which suffix is used to refer to the study of a particular subject?

The suffix that indicates the study of a particular subject is "-ology." This suffix is derived from the Greek word "logos," which means "study" or "discourse." When attached to a root word, it signifies a field of knowledge or a branch of learning, as seen in terms like "biology" (the study of life) and "psychology" (the study of the mind).

The other suffixes do not convey the same meaning. For example, "-pathy" refers to disease or suffering and is often used in words like "pathology," which relates to the study of diseases. "-ectomy" indicates the surgical removal of a part of the body, as in "appendectomy," which involves the removal of the appendix. Lastly, "-itis" denotes inflammation, common in medical terminology describing conditions like "arthritis" (inflammation of the joints). Thus, "-ology" is the only suffix among the options that specifically relates to the study of a subject.