Which of the following best defines a combining vowel?

A combining vowel is specifically a vowel, typically the letter 'o', that is used between root words or a root word and a suffix to facilitate pronunciation and enhance the fluidity of speech when forming complex medical terms. This vowel helps to bridge the two parts of the term, making it easier to say and interpret. For instance, in the term "gastroenterology," the combining vowel 'o' appears between the root words "gastro" (stomach) and "enter" (intestine) to enhance clarity and pronunciation.

The other options do not accurately describe a combining vowel. A consonant doesn’t serve this function, and suffixes, while they can add detail or modify meaning, do not function as connecting elements in the way that a combining vowel does. Similarly, a prefix modifies the meanings of the root words but does not facilitate the connection or pronunciation between them. Thus, the definition of a combining vowel centers on its role in pronunciation, making the correct answer the one that highlights this aspect.