Specialist (noun)

1. A person who has a high degree of skill or knowledge in a particular area.
2. A person who has expertise in a particular subject or activity.
3. A person who specializes in a particular field of medicine, science, or technology.

Origin:

Early 17th century: from french spécialiste, from old french especial "particular", from latin specialis.

Examples:

1. The company hired a specialist to fix the problem.
2. She was a specialist in medieval literature.
3. He was referred to a specialist for a second opinion.
4. The specialist was able to diagnose the rare condition.
5. She was a specialist in early childhood development.