Step 1: Understanding the Concept:
"Neophyte" is a noun that means a person who is new to a subject, skill, or organization, someone just starting out.
Step 2: Key Formula or Approach:
To find an antonym, we look for a word that sits at the opposite end of the same scale, here the scale of experience, running from "brand new" to "highly experienced".
Step 3: Detailed Explanation:
"Student" still suggests someone in the process of learning, so it sits closer to "neophyte" than opposite it.
"Clown" describes a role or personality trait unrelated to experience, so it does not belong on the experience scale at all.
"Professional" often implies skill, but a person can be a professional and still be new to a role, so it does not guarantee the opposite of "beginner".
"Veteran" specifically means a person who has spent a long time in a field and built up deep experience, placing it at the far opposite end of the scale from "neophyte".
Step 4: Final Answer:
"Veteran" is the word that means the opposite of "neophyte", so option (C) is correct.
\[ \boxed{\text{veteran}} \]