From Longman Business Dictionary
specialistspe·cial·ist /ˈspeʃəlɪst/ noun [countableC]1COMMERCEa person or business that has a lot of skill or knowledge in a particular subject, and often gives advice to othersspecialist inHe’s a specialist in the insurance industry.
Many technical specialists are employed in commerce and the service sector.
2American EnglishAmEFINANCE a dealer on a stockmarket who buys and sells shares in a small list of companies for investors —specialist adjectiveadj [only before a noun]The advantage of employing a specialist firm is that its tradesmen are more likely to be well trained and experienced.