Which of the following definitions best fits a suffix?

A suffix is defined as a word part that is added to the end of a root word to modify its meaning or create a new word. This makes option C the correct answer, as it captures the essence of how suffixes function in language—by enhancing or expanding the meaning of the root. For example, adding the suffix "-itis" to the root "append" creates "appendicitis," which indicates inflammation of the appendix.

The other options do not accurately describe a suffix. The first option refers to a prefix, which is a word part added to the beginning of a root word. The second option describes a standalone word, which does not involve modification or addition to another word. The fourth option implies a general category of terms rather than specifically defining what a suffix is. Therefore, option C stands out as the best fit for defining a suffix.