Which word describes a person who is a beginner in a particular activity or field?

The word that best describes a person who is a beginner in a particular activity or field is "novice." This term specifically refers to someone who is new and lacks experience in a certain area, emphasizing their status as someone who is just starting to learn or engage in that activity.

In contrast, the other terms denote varying levels of expertise and experience. An "expert" implies a person with extensive knowledge and skills acquired over time, while a "veteran" refers to someone who has significant experience, often in a specific field or profession. "Master" indicates a high level of proficiency and command over a particular skill or discipline, which is far from the beginner status of a novice. Thus, "novice" is the most appropriate term to describe someone at the very beginning of their journey in a specific activity or field.