Which suffix signifies treatment in medical terminology?

The suffix that signifies treatment in medical terminology is -therapy. This suffix is derived from the Greek word "therapeia," meaning "treatment." It is commonly used in various medical terms to describe specific treatment modalities or therapies aimed at addressing health conditions. For instance, terms like psychotherapy, chemotherapy, and physiotherapy use this suffix to indicate the type of treatment being administered.

The other options do not carry this meaning. The suffix -auto refers to self, -logous relates to study or science (as in the study of something), and -o is typically just a linking vowel used to connect root words in medical terminology. Therefore, -therapy is the only suffix among the choices that specifically denotes a form of treatment.