Which term best defines an expert with specialized knowledge and skill?

The term that best defines an expert with specialized knowledge and skill is "professional." This designation typically refers to individuals who have undergone extensive education or training within a specific field, allowing them to attain a high level of expertise and competence. Professionals often adhere to established standards, codes of conduct, and ethical guidelines pertinent to their area of expertise.

While the other terms may reflect aspects of skills or knowledge, they do not capture the same breadth of commitment to ongoing development and ethical standards that characterize a professional. For instance, "a practitioner" refers to someone actively engaged in a profession or activity but does not inherently imply the level of expertise or formalized training associated with being a professional. "A specialist" usually refers to someone with a focused area of expertise but can lack the comprehensive qualifications or recognition that a professional holds. "An artisan" typically denotes someone skilled in a craft but does not encompass the formal knowledge and ethical responsibilities pertinent to professional roles across various fields. Thus, "professional" is the most accurate term in this context.