What is the technical term applied to any deformity of the nail?

The term "onychos" is derived from the Greek word for nail, and "osis" typically refers to a condition or disorder. Therefore, onychosis is specifically used in medical terminology to describe any deformity, abnormality, or disease affecting the nails. This could encompass a range of issues, such as changes in nail shape, color, structure, or growth patterns.

The other terms listed relate to different conditions. Dermatitis refers to inflammation of the skin and does not apply directly to nail conditions. Fungus generally refers to a type of organism that can infect or cause conditions in various parts of the body, including nails, but it does not describe a deformity itself. Paronychia is a specific infection around the nail and is not a general term for nail deformity. Thus, onychosis is the most accurate term among the choices for describing any deformity of the nail.